Optional Science Book Class 10

2. When a rod of paramagnetic material is Suspended
suspended freely between two magnetic poles,
then it slowly turns to set itself parallel to the N S
magnetic field. The poles developed at the end
of the rod are opposite to the nearer magnetic S
poles.
paramagnetic substance

fig: paramagnetic substance in a magnetic field

3. In a non-uniform magnetic field, the paramagnetic substance is attracted towards the
stronger part of the field. That is, the paramagnetic material moves from weaker to
stronger parts of the magnetic field.

For example, when a paramagnetic liquid taken in a watch glass

or glass crucible is placed over two nearby magnetic poles,

then the liquid rises in the middle where the field is strongest

as shown in the given figure. When the distance between the

pole pieces is increased, the effect is reversed. That is the liquid

depresses in the middle and rises near the edges, because now

the field is strongest near the poles. fig:paramagnet liquid in a
4. When a bar of paramagnetic material is placed in a magnetic field, the linmeagsnoetficfofierlcde tend

to accumulate in it as shown in the given figure.

Ferromagnetic substances:

Substances which when placed in an external magnetic field acquire strong magnetization in

the direction of the applied magnetic field are called ferromagnetic substance. For example,

iron (Fe), cobalt (Co), nickel (Ni), magnetite (Fe3O4), gadolinium (Gd), dysprosium (Dy) and
their alloys.

Properties of ferromagnetic substances

Ferromagnetic substances show properties of a paramagnetic substance to a much greater
degree. The following are the properties of ferromagnetic substances:

1. These substances when placed in a magnetic field, are strongly magnetized in the
direction of the field. So they are even attracted by a weak magnet.

2. When a rod of paramagnetic material is suspended freely between two magnetic poles,
then it rotates and finally sets itself parallel to the magnetic field.

3. In a non-uniform magnetic field, the ferromagnetic substance is attracted towards the
stronger part of the field.

4. The magnetic lines of force tend to crowd into the ferromagnetic substance.

Magnetic flux

In class 9 optional science, you had drawn magnetic lines of force around a bar magnet.
Magnetic lines of force are imaginary curved lines which enter into the south pole from the
north pole of a magnet. Such lines of force never intersect each other. The tangent at any
point on the magnetic lines of force gives the direction of the magnetic field at that point. The
magnetic lines of force are around magnets as well as a current carrying coil. Shape of the
magnetic lines varies according to the source of magnetic field. The shape of the magnetic
lines of force gives us an idea about the magnetic field around a source.

Optional Science - 10 101

PHYSICS

~ !Iij ;-•1:•j)(?tr·n

Current wire Solenoid Bar Magnet The Earth
in wire

fig:magnetic field sources fig:magnetic flux

A surface inside a magnetic field receives magnetic lines of force. We look after the number
of magnetic lines of force falling over a surface to know the effect of the magnetic field. The
term used in physics to measure the magnetic field strength over a given area is magnetic
flux. Therefore, magnetic flux is defined as the total number of magnetic lines of force passing
normally through any surface inside the magnetic field. Magnetic flux is denoted by Φ. The
magnetic flux through area ‘A’ at right angles to the magnetic lines of force is given by

Φ = BA

Where ‘B’ is the magnetic field strength normal to the surface area ‘A’.

a. SI unit of magnetic flux: The SI unit of magnetic flux is the weber. Its symbol is Wb.
The unit weber is given after the German physicist and co-inventor of the telegraph,
Wilhelm Weber.

b. Variation of magnetic flux: The magnetic flux is proportional to the number of field lines
that pass through a surface. If a magnet, or a coil, is moved closer to one another, then
the magnetic flux through the surface of the coil increases. Conversely, the magnetic
flux decreases when it is moved away from one another.

Electromagnetic induction

A magnetic field exists in the region around a current L__i§j g~g~ ! Magee< mosiagdowa I Magae, mo,iag ,p
carrying conductor, such as a wire. Moving a conductor
in a magnetic field is the basis for a simple electric I , ,) CoU
generator. When a conductor is moved in a magnetic al,aaome<"
field in such a way that it intersects the magnetic lines of Cfo,,,aaome,e, CoU
force perpendicularly, then the magnetic flux linked with

the circuit gets changed. This change in magnetic flux fig: electromagnetic Induction through a coil

causes an electric current to flow through the conductor. Such effect is called electromagnetic

induction. The process of obtaining an induced emf in a closed circuit by changing the

magnetic flux linked with it is called electromagnetic induction.

Memory Plus

If there is a relative motion between a magnet and a coil, an emf is induced in the coil.

Activity- 6.
1. Make a coil by winding about 50 turns of thin insulated copper

wire round a cylindrical object.
2. Connect the two terminals of the coil with a galvanometer.

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PHYSICS

3. Move a pole of a bar magnet in and out of the coil and observe the deflection of the
needle in the galvanometer.

4. Investigate how the magnitude of the induced current depends on (i) the speed of the
relative motion, (ii) the strength of the magnet,(iii) the number of turns on the coil

The given experiment shows that

1. When a magnet is moved quickly into a coil a large current gets induced.

2. When a powerful magnet is used, the magnitude of the induced current increases. This
is because a more powerful magnet has more lines of force between its poles. So when
a wire moves through the field, it cuts the magnetic lines of force more often.

3. When the number of turns in a coil increases, the induced emf also increases.

4. In the above activity, if the magnet is moved away from the coil with the south pole
pointing towards the coil, then it produces deflection in the opposite direction as
compared to the case when the magnet is moved towards the coil.

Faraday’s laws of electromagnetic induction

Electromagnetic induction was discovered in 1831
by Michael Faraday. He was the first to observe
how the magnitude of an induced emf depends
upon the rate of change of magnetic flux. On the
basis of the observations made in his experiment,
Faraday formulated the following laws.

a. Whenever the magnetic flux linking a coil fig: electromagnetic induction
changes, then an emf is induced in the coil.

b. The magnitude of the induced emf is directly proportional to the rate of change of the
magnetic flux.

c. The induced emf lasts as long as there is a relative motion between the magnet and the
coil.

Faraday observed the deflection of the galvanometer needle in the opposite direction when
the direction of the motion of the conductor was changed. This is due to the change in the
direction of the induced current while changing the direction of motion of the conductor in
between the two magnetic poles. The direction of the induced current in electromagnetic
induction is given by Fleming’s right hand rule.

Know the Reason

A stationary magnet does not induce a current in a coil, why?

In the case of a stationary magnet, the magnetic flux linked with a closed circuit or a coil
remains constant. When it is moved to and fro, the magnetic flux linked with the closed
circuit changes and an emf. gets induced. So a stationary magnet does not induce a current
in a coil.

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Fleming’s right hand rule

Fleming’s right hand rule is used to predict the direction of e;,,aJ
an induced current in electromagnetic induction. According
to Fleming’s right hand rule, if we stretch the right-hand Induced current
thumb, fore finger and middle finger perpendicular to one
another and point the thumb in the direction of the motion of fig:Flemings right hand rule
the conductor, the fore finger in the direction of the magnetic
field, then the middle finger indicates the direction of the
induced current from electromagnetic induction.

Applications of electromagnetic induction

Many electrical devices operate on the principle of electromagnetic induction. The bicycle
dynamo and generator are the most important devices based on electromagnetic induction.

Bicycle dynamo
Activity:

Take a bicycle with dynamo lights. .....-rotating
Push the driving wheel of your - - ridged knob
bicycle dynamo towards the tyre.
Lift the wheel of your bicycle and magnet
make sure that it rotates freely.
Observe the brightness of the light ~iron core
when the wheel is rotating slowly.
Now rotate the wheel faster to copper
observe the brightness of the bulb coil
in this case, too.
to light

connection to

bicycle frame

fig:bicycle dynamo

1. What changes do you observe in each case?

2. Does the induced current last for a long time in the wire?

The brightness of the dynamo light increases with the increasing speed of the bicycle
wheel. It is due to the increased rate of change of the magnetic flux. Such induced
current in the wire lasts as long as the bicycle wheel rotates.

Dynamos convert mechanical energy into electrical energy. A bicycle dynamo is a very simple
dynamo in which a magnet is made to spin around near a fixed coil.

i. Principle of a bicycle dynamo:The working principle of a bicycle dynamo is based on
electromagnetic induction, i.e., whenever the magnetic flux linked with a closed circuit
changes, an electromotive force, or emf, gets induced in the circuit. As a result, electrical
current is obtained from the two terminals of the coil used in the bicycle dynamo.

ii. Construction: A bicycle dynamo has a cylindrical permanent magnet with poles on
opposite sides of the cylinder, which is fixed on an axle attached to the driving wheel.
Its coil is fixed on the iron core. Both the coil and magnet are sealed in a metal case.

iii. Working mechanism: When the driving wheel of a dynamo rubs against the tyre, it
rotates the cylindrical magnet inside the bicycle dynamo. Due to this, the magnetic flux
linked with the coil changes and an emf gets induced in the coil.

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Generator

An electric generator is a device that converts mechanical energy into electric energy. It is used
to generate electricity on a large scale. In a generator, an armature is rotated in a magnetic field
at a high speed to generate electric current on a large scale.

Principle of generators

The working principle of generators is based on electromagnetic induction, i.e., whenever
the magnetic flux linked with a closed circuit changes, an emf gets induced in the circuit. As
a result, electrical current is obtained from the two terminals of the coil used in a generator

Types of generators: AC and DC generators are the two types of generator.

AC generator

An alternating current generator is called an AC generator. In alternating current, the
electrons flow forward and backward. The current whose direction changes periodically and
whose magnitude also varies continuously is called an alternating current. An AC generator,
bicycle dynamo, etc. are sources of AC. In an AC generator, the ends of the coil windings are
connected to two slip rings. Turning the coil at a steady speed produces an alternating current
(AC), which changes its polarity periodically, and the magnitude remains variable.

Construction of an AC generator

Penna,~ent Rectang ular
magnet coil

fig:construction of a.c. generator

An AC generator is consists of four main parts:
a. Coil or armature: In an AC generator, there is a rectangular coil ABCD with a large

number of turns of insulated copper wire over a soft iron core. It is also called an
armature. The soft iron core used in the armature increases the magnetic flux.
b. Magnetic field: It is usually the field developed by a strong horse shoe type magnet
having concave poles. The coil can be rotated rapidly in between the north pole (N) and
south pole (S) of the strong magnet with the help of a shaft. The axis of the armature is
perpendicular to the magnetic field lines.

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c. Slip rings (R1 and R2): The slip rings used are two circular pieces of copper. The two
ends of the copper wire in the coil are connected to slip rings R1 and R2. These rings
rotate with the coil to draw current from the generator.

d. Carbon brushes (B1 and B2): Slip rings are tightly kept in contact with two carbon
brushes B1 and B2. Each slip ring rubs against a brush. This type of contact makes good
electrical contact to conduct electricity when the two slip rings R1 and R2 are rotated
with the coil.

Working of an AC generator

As the coil rotates in a magnetic field, an alternating emf is induced across its two ends. This
causes a flow of alternating current in the coil. The current produced in the rotating coil can be
tapped out through the slip rings into the carbon brushes. From the carbon brushes, current is
taken out through the wires.

From the given figure showing the construction of an AC generator, when the coil ABCD is

rotated in a clockwise direction between the north pole (N) and the south pole (S) of a strong

magnet, the arm AB of the coil moves up, cutting the magnetic lines of force near the N-pole

of the magnet. On the other side, the arm CD of the coil moves down, cutting the magnetic

lines of force near the S-pole of the magnet. According to Fleming’s right hand rule, the

induced currents are in the directions A to B on the arm AB and C to D on the arm CD. Thus,

the induced current on the two sides of the coil are in the same direction, and we get an

effective induced current in the direction ABCD. +ve maximum value
+I

In each cycle of an alternating current, the current changes Current (I)

its direction twice. When we say the frequency of an AC is 50 Alternating

Hz, it means the current changes its direction 100 times in one time (t)

second. The alternating current supplied in our country has a —I
frequency of 50 Hz.
—ve maximum value

fig:current-time graph for a.c.

DC generator

A direct current generator is called a DC generator. If the electrons always flow in the same

direction and the direction of a current remains unchanged in a conductor, it is called a direct

current. A cell has fixed positive and negative electrodes. The current flowing from a cell is

DC. A dry cell, photo cell, solar panel are sources of DC. Rectangular Rotation of coil
coil anticlockwise

Construction of a DC generator M B C

As in an AC generator, a DC generator Permanent current
also consists of four main parts. If we magnet current

replace the slip rings of an AC generator Field
by a commutator, then it will become a DC
field

generator. N A motion S

a. Coil or armature: In a DC generator, R1 D
there is a rectangular coil ABCD with R2 Commutator
a large number of turns of insulated
copper wire over a soft iron core. +B1 Carbon brush G
—B2 Galvanometer

fig:construction of d.c. generator

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b. Magnetic field: It is usually the field developed by a strong horse shoe type magnet
having concave poles. The coil can be rotated rapidly in between the north pole (N) and
south pole (S) of the strong magnet with the help of a shaft.

c. Half ring or split rings (R1 and R2): The split rings used are two semi-circular pieces of
copper. The two ends of the coil are connected to the two copper half rings or split rings
R1 and R2 of a commutator.

d. Carbon brushes (B1 and B2): Split rings are tightly kept in contact with two carbon
brushes B1 and B2. Each split ring rubs against a brush. This type of contact makes good
electrical contact in conducting electricity when the two split rings R1 and R2 are rotated
with the coil. The two half rings R1 and R2 touch the two carbon brushes B1 and B2 one
by one.

Working of a DC generator

The current produced in the rotating coil can be tapped out through the commutator half rings
into the carbon brushes. From the carbon brushes, current is taken out through wires.

From the given figure showing the construction of an AC generator, when the coil ABCD is
being rotated in an anticlockwise direction between the north pole (N) and south pole (S) of a
strong magnet, the arm AB of the coil moves down, cutting the magnetic lines of force near the
N-pole of the magnet. On the other side, the arm CD of the coil moves up, cutting the magnetic
lines of force near the S-pole of the magnet. According to Fleming’s right hand rule, the
induced currents are in the directions B to A on arm AB and D to C on arm CD. Thus, the
induced current on the two sides of the coil are in the same direction, and an effective induced
current in the direction DCBA. Direct current is obtained from the two terminals of the carbon
brushes as

i. One carbon brush (B1) is at all times in contact with the
coil arm moving down in the magnetic field. Due to this,

the brush B1 becomes a positive (+) pole of the generator.

ii. Another carbon brush (B2) always remains in contact C Time ~

with the coil arm moving up in the magnetic field. Due u:, ~

to this, the brush B2 becomes the negative (-) pole of the fig:current-time graph for d.c.

generator.

Due to this, the current in the outer circuit always flows in one direction. So, it is direct current.

Methods to increase the induced emf from a dynamo and generator

a. By increasing the number of turns in the coil.
b. By decreasing the distance between the coil and magnet.
c. By using a powerful magnet. It increases the strength of the magnetic field.
d. By increasing the rate of change of the magnetic flux. This can be done by rotating the

coil or magnet faster.

PHYSICS 0Optional Science - 10 107

Motor effect

In 1820, Hans Christian Oersted discovered that electric currents cause magnetic fields around
them, which is the magnetic effect of an electric current. The given figure shows an electric
field around a straight current carrying current. It is a circular field.

When a wire carries an electric current through another ~agnetic fields ~ current
magnetic field, then the two magnetic fields interact. There direction
is mutual attraction or repulsion due to the magnetic I~ the opposite
field developed between a current carrying conductor direction attract.,.;:-r magnetic
and magnetic field of the magnet. French scientist Andre fields in
Marie Ampere in 1820 demonstrated this force. The forces ~the same
between the two magnetic fields can move wires or turn direction
the coil which carry an electric current. Thus, when a
freely suspended current carrying conductor is kept in a repel
magnetic field then it comes in motion. This effect is called
motor effect. wire pushed

in this

direction wire

fig:motor effect

Activity- 6.

1. Take a conductor and a conducting wire. SB
A
2. Make a support of the conducing wire at two points ‘A’ and
‘B’. N

3. Hang the conductor from a stand as shown in the given figure
and connect the two terminals of the conductor to a battery.

4. Bring a U-shaped magnet close to the conductor. Do you
observe movement in the conductor?

The movement in the conductor is due to the motor effect.

Electric motor:

An electric motor represents the transformation of energy from one form to another. An
electric motor is a device which converts electric energy into mechanical energy. It is an
application of motor effect. In an electric motor, electricity passes through a coil of wire,
producing a magnetic field around it.

computer fan electric mixture fan immersion motor water lifting pump washing machine

Principle of electric motor

It is based on the principle of motor effect, i.e., when a rectangular coil is placed in a magnetic
field and current is passed through it, a turning effect acts on the coil, which rotates it
continuously to convert electrical energy into mechanical energy.

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Types of electric motor

DC motor

A DC motor is a common type of motor that is powered by direct current. For example, the
motor of battery- operated toys, motors in electronic devices like DVD players, computers,

Construction: A DC motor consists of the following parts:

i. Armature: A DC motor consists of a coil with a large number of turns of insulated
copper wire over a soft iron core. This coil wound on the soft iron core forms the
armature. The coil is mounted on an axle and is placed between the cylindrical concave
poles of a magnet.

ii. Magnetic field: A permanent magnetic field is around the armature.

iii. Half ring or split rings (R1 and R2): The split
rings used are two semi-circular pieces of copper.

The two ends of the coil are soldered to the two

copper half rings or split rings R1 and R2 of a
commutator. It is used to reverse the direction of

flow of current. They rotate along with the coil.

iv. Brushes: Two carbon brushes (B1and B2) in contact
with the commutator make a tight connection to

conduct electricity. A battery is connected to the

brushes which are in contact with the rings. Termlnals

fig: construction of d.c. motor

Working of DC motor Thrust

When the coil is powered, a magnetic field is generated around

the armature. According to the Fleming’s left hand rule, the

left side of the armature is pushed away from the N-pole of the
Fhced carbon

magnet and drawn towards the right, causing rotation. When brushes

the coil turns 900, the brushes lose contact with the commutator,

and the current stops flowing through the coil. However the

coil keeps turning because of its inertia of motion.

Now when the coil turns 1800, the sides get interchanged. That fig:working of a d.c. motor

is, the left side of the armature is now at the right side. As a result, the split ring R1 is now
in contact with brush B2 and split ring R2 is in contact with brush B1. Therefore, the current
continues to flow in the same direction. This ensures that the turning effect on each coil is

always in the same direction.

AC motor

An AC motor is powered by alternating current. For example,

the motor in a driller machine, vacuum cleaner, water lift

pump, etc. Though the working principle of the AC motor is

the same as that of a DC motor, there are some differences in

their construction and working mechanism. The polarity of

AC changes periodically and its magnitude varies. Thus, the fig: a.c. motor

magnetic field produced by the electromagnets also changes its direction at the same time.

This dual switching at the same time causes the direction of turning force on the coil to remain

the same.

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Memory Plus

An AC motor runs at a fixed speed that is determined by the frequency of AC supply. On
the other hand, DC motor has speed-control capability.

Differences between DC and AC motors AC motor
The field magnet is an electromagnet.
DC motor Slip rings are used.
The field magnet is a permanent magnet. They are powered by an alternating current.
Split rings or commutators are used.
They are powered by a direct current.

Applications of electric motor
Electric motors are used in many ways in our daily lives.

i. Electric fan rotates due to the motor in it.

ii. Electronic devices like computers, DVD players have motors in them.

iii. Water lifting pump consists of a motor.

iv. Saw mills, rice mills have powerful motors.
Comparison of DC generator with DC motor
The construction of a DC generator is the same as that of a DC motor. But their working
mechanism is just the opposite to one another. In a DC generator, we rotate the coil and
produce direct current whereas in a DC motor, we do apply direct current and rotate the coil.
If a DC generator is connected to a battery, it will work as a motor. Conversely, if a motor coil
is made to rotate, then it will work as a DC generator and produce direct current at the brushes.

Memory Plus

The DC generator, or DC dynamo, consists of two half rings. If the half rings are replaced
by slip rings then they will change correspondingly into AC generator and AC motor.

Differences between electric motor and electric generator

Electric motor Electric generator

1. It converts electric current into 1. It converts mechanical energy into electric

mechanical energy. current.

2. Current is supplied to the coil placed in 2. The coil is rotated in the magnetic field by an
a magnetic field by an external source. external source.

3. It is based on the motor effect. 3. It is based on the principle of electromagnetic
induction.

Transformer

Electromagnetic induction can be used to transfer electrical energy from one circuit to another
by means of a magnetic field which links the two coils. The two coils are called primary coil
and secondary coil.

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An induced emf appears in the secondary coil when there is a change of current in the primary
coil. There are two ways of changing the current in the primary coil.

1. Direct current (DC) in the primary coil can be switched on and off rapidly by an
automatic mechanism.

2. An alternating current (AC) can be used in the primary coil. Its magnitude and direction
change periodically. This mechanism of obtaining an induced emf in a secondary coil
by passing an alternating current in the neighboring coil (primary coil) is called mutual
induction. A transformer is based on the principle of mutual induction.

The transmission of electricity involves transferring energy over a long distance. In a
hydropower station or nuclear power plant, electricity is first generated at a lower potential
difference. It must be stepped up to a high voltage like 12,000 V for its transmission. When
electricity enters a building or home, the high voltage alternating current (AC) should be
stepped down to a low voltage like 220 V. A transformer is a device for increasing or decreasing
an AC voltage. Transformers are essential in the transmission of electricity from a power
station to the customers.

Construction Applied laminated soft-iron core
a.c. supply
A transformer has two coils fixed to a soft-iron
core. The main part of a transformer are,

a. Primary coil: It is the coil connected to the n2
alternating current source. The number of
n1 Load

windings in the primary coil are called

primary turns (n1) and the AC voltage primary voltage(V1) secondary voltage (V2)
supplied in the primary coil is called
primary turns (n1) secondary turns (n2)
primary voltage (V1).
fig:construction of a transformer

b. Secondary coil: It is the coil through which the stepped-up or stepped-down AC voltage
is obtained. The number of windings in the secondary coil are called secondary turns
(n2) and the AC voltage supplied in the secondary coil is called secondary voltage (V2).

c. A soft iron laminated core: A block

made from U-shaped iron strips or E and

I shaped iron strips to fix the primary Solid
Core

coil and secondary coil of a transformer

is called the core. The process of joining

polished U-shaped iron strips together is fig:with no lamination fig:lamination of core
called lamination of the core. Shellac and high eddy current of a transformer

varnish are used to polish the iron strips.

Know the Reason

The core of a transformer is laminated so that layers of soft iron are separated from
one another by layers of insulating material. Due to lamination of the core, induced
currents (i.e., eddy currents) in the core are reduced. It causes the flux from the
primary coil as high as possible.

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Working principle of a transformer

A transformer is based on the principle of mutual induction. In a transformer, an alternating
current passes through the primary coil when it is connected to an AC source. The magnetic
field due to AC in the primary coil changes in both magnitude and direction. This changing
magnetic field changes the magnetic flux linked with the secondary coil. The core provides
magnetic path for the flux, to get linked with the secondary winding. According to Faraday’s
laws of electromagnetic induction, whenever the magnetic flux linked with a closed circuit
changes, an emf gets induced from two terminals of the secondary coil. Transformers are
designed so that all the magnetic flux produced by the primary coil passes through the
secondary coil.

A transformer is based on the following two laws:

i. According to the law of conservation of energy, the power input in the primary coil (P1=
I1V1) is equal to the power output in the secondary coil (P2 = I2V2).

ii. The magnitude of induced emf is directly proportional to the ratio of number of turns
in the secondary coil (n2) to the number turns in the primary coil (n1).

Know the Reason

A transformer does not work with DC, why?

Instead of AC, if DC is supplied in the primary coil then the magnetic field produced is of
constant strength. Due to this, the number of magnetic lines of force which are intersected
by the secondary coil does not change. In such a condition, current does not get induced
from the two terminals of the secondary coil. So a transformer does not work with DC.

Energy losses in a transformer

An ideal transformer is a theoretical and linear transformer. It is lossless and perfectly coupled;
i.e, there are no energy losses and flux is completely confined within the magnetic core. In case
of a real transformer, there are following possible energy losses.

a. Eddy current losses: In a transformer, the alternating current (AC) in the primary coil
produces a changing magnetic field. Due to this changing magnetic field, eddy currents
are induced in the soft-iron core of the transformer. These currents could cause the core
to become very hot. The possible loss of energy can be reduced by the design of the
transformer. For this, the core is made of thin sheets of iron called lamination, separated
by insulating material. This makes it much harder for the eddy currents to flow.

b. Copper losses: Generally the primary coil and secondary coil of a transformer are
made of copper wire. They have resistance. When current flows through these wires, a
part of the energy is lost in the form of heat. This energy lost through the windings of
the transformer is known as copper loss. The use of thick wires for windings can reduce
copper loss.

c. Flux losses: In a transformer, the magnetic flux linked with the primary coil is not
equal to the magnetic flux linked with the secondary coil. Most of the flux gets linked
with the secondary winding which is called as ‘useful flux’ or main ‘flux’, and the flux
which does not get linked with secondary winding is called as ‘leakage flux’.

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d. Losses due to vibration of core: A transformer in operation produces a humming
noise. Some of the electrical energy supplied is wasted in the form of mechanical energy
during vibration of the core, which produces sound.

Transformer formula

The transformer formula relates primary voltage (V1), primary turns (n1), secondary voltage
(V2) and secondary turns (n2) in a transformer as:

Secondary voltage (V2) = Secondary turns (n2)
Primary voltage (V1) Primary turns (n1)

This formula is used to count the number of turns in the primary coil and secondary coils

while manufacturing a transformer.

Solved numerical- 6.

In a transformer, the ratio of secondary turns to primary turns is 4:3. Which type of transformer
is it? Find the secondary voltage when the transformer is connected to a power supply of 220 V.

Solution:

Here, the ratio of secondary turns to primary turns (n2:n1) = 4:3
This type of transformer has more turns in the secondary coil. So it is a step-up
transformer.

Primary voltage (V1) = 220 V
Secondary voltage (V2) = ?
According to the transformer formula

Secondary voltage (V2) = Secondary turns (n2)
Primary voltage (V1) Primary turns (n1)

Or V2 = 4
220 3

Or V2 = 4 × 220 = 293.33 V
3

Therefore, the secondary voltage is 293.33 V.

Solved numerical-

A step-up transformer has 10,000 turns on its secondary coil and 100 turns on its primary
coil. An alternating current of 5 A flows in the primary coil when it is connected to a 12 V AC
supply. Calculate

1. The power input to the transformer

2. The emf induced across the secondary coil.
Solution

Here, Primary voltage (V1) = 12 V
Secondary voltage (V2) = ?
Primary current (I1 ) = 5 A
Secondary turns (n2) = 10,000
Primary turns (n1) = 100

PHYSICS 0Optional Science - 10 113

Now, (i) Input power = I1V1 = 5 × 12 = 60 W
(ii) Secondary voltage is given by the formula

Secondary voltage (V2) = Secondary turns (n2)
Primary voltage (V1) Primary turns (n1)

Or, V2 = V1 × n2 = 12× 10000 = 1200 V
n1 100

Therefore, the emf induced across the secondary coil is 1200V.

Types of transformers

There are different types of transformers on the basis of number of windings, construction, their
purpose, types of supply, their use, coolant material used, etc.

a. On the basis of construction : Core type transformer and shell type transformer

b. On the basis of their purpose: Step up transformer and tep down transformer

c. On the basis of type of supply: Single phase transformer and three phase transformer

d. On the basis of their use: Power transformer, distribution transformer and instrument
transformer

e. On the basis of cooling employed: Oil-filled self cooled type; oil-filled water cooled type
and air blast type (air cooled)

Here, in class 10 optional science, you will learn about the types of transformers on the basis of
number of windings. Step-up transformer and step-down transformers are the two types of
transformers on the basis of windings.

Step-up transformer: High potential difference is required for Laminated Iron Core

transmission of electricity from a hydropower station over long fig:step up transformer
distances. The transformer which converts the applied low voltage
AC to high voltage AC is called a step-up transformer. It is designed
with more numbers of secondary turns than primary turns, i.e., n2
> n1. So the secondary voltage is stepped up compared with the
potential difference applied to the primary coil.

Applications

i. It is used to obtain high voltage of about 15000 V to accelerate the electron beam in a
Cathode Ray Tube (CRT) from 220 V.

ii. In a hydropower station or nuclear power plants, the low voltage AC is stepped up to a
high voltage like 12 kV (12,000 V) by using a step-up transformer for its transmission.

iii. In a microwave oven, a step-up transformer changes the input voltage of about 120V-240V
to around 5000V.

iv. An inverter transformer converts low voltage from the battery to 220-240V AC.

Step-down transformer: We need a device to run a 3V radio from L~ ~

a 220V AC. Such a device lowers the AC voltage to the desired level.

The transformer which converts the applied high voltage AC to low

voltage AC is called a step-down transformer. It is designed with Pri~

less numbers of secondary turns than primary turns, i.e., n2 < n1. So fig:Step down transformer
the secondary voltage is stepped down compared with the potential difference applied to the

primary coil.

0114 Optional Science - 10

PHYSICS

Applications:

i. In a distribution substation, a step down transformer is used to lower the high voltage AC
from the power station to 220V for domestic use.

ii. Battery chargers like a cell phone charger has a step-down transformer, which reduces 220
V to between 3 V and 9V.

Differences between step-up transformer and step-down transformer

Step-up transformer Step-down transformer

The windings in the secondary coil are The windings in the secondary coil are less

more than those in the primary coil. than those in the primary coil.

It converts low voltage AC at high current It converts high voltage AC at low current into

into high voltage AC at low current. low voltage AC at high current.

Resistor

A resistor is a two-terminal electrical component that adds electrical resistance to limit or
regulate the flow of electrical current. In electronic circuits, resistors are used to reduce current
flow, adjust signal levels, to divide voltages, etc. The value of the resistances used in electrical
and electronic circuits varies over a wide range.

Connection of resistors/ electrical devices

You may have seen that a number of resistors connected together in a specific way on the
board of electronic devices. Also in our domestic circuit, there are a number of electric loads
like bulbs, a TV, fan, refrigerator, electric motor, etc. Such loads also offer resistance to the flow
of electrons. They are connected to the same main power supply to our home. There are two
ways to connect two or more resistors or electrical devices together in a circuit. They are series
connection and parallel connection.

Series connection

In a series circuit, two or more appliances are connected so as to provide a single conducting
path for current. Thus, the same current flows through all of the resistors in the connection.
When two or more resistors in a circuit are connected from end to end in order to get the same
current flowing through each of them in succession, then the resistors are said to be connected
in series connection. For example, the decorative lights used to illuminate during Dipawali,
Christmas, etc.

Expression of the equivalent resistance in a series connection of resistors

In the given circuit diagram, three resistors of resistance R1, R2 and R3 are connected in series
with a source of potential difference ‘V’. Let a current ‘I’ flow through the circuit.

From Ohm’s law, the potential differences across the three resistances is given by

V1 = IR1, V2 = IR2, V3 = IR3

If R be the equivalent resistance of the series connection, then on applying a voltage ‘V’ across

it, the same current ‘I’ must flow through it. -v----
So, V = IR
But V = V1 + V2 + V3 -+---V I_. -+--V2____..._y 3----+

Or IR = IR1 + IR2 + IR3 -~R, -Rz---

∴ R = R1 + R2 + R3 fig:series connection of resistors

Optional Science - 10 115

PHYSICS

Characteristics of series connection of resistors

The following are some important characteristics of series connection of resistors:

1. There is a single conducting path for all the resistors in a series circuit.

2. The potential difference across individual resistors is not the same. The net potential
difference between the two ends of the combination is equal to the sum of the potential
difference between the individual resistors. i.e.,
V = V1 +V2 +V3

3. The current through the different resistors is the same.
4. The total resistance in a series circuit is equal to the sum of separate resistances in the

circuit. i.e.,
R = R1 +R2 +R3.

Disadvantages of series connections

In a series circuit, resistors or electric loads are connected one after another. So

1. A separate switch cannot be used for individual resistors. It is not possible to operate
the resistors independently.

2. If just one resistor stops working due to some defect, then all other resistors in the
circuit fail to function.

3. Each resistor does not get the same voltage.

4. The overall resistance of the resistors gets increased. Due to this, the current from the
power supply is low.

Parallel circuit

In a parallel circuit, two or more appliances are directly connected to a source of electricity.
Each resistor has an individual path for the flow of current. Thus, electric current divides
in a parallel connection of resistors. When two or more resistors in a circuit are connected
between two common points in order to get different currents, then the resistors are said to be
connected in parallel connection.

Expression of equivalent resistance in a parallel connection of resistors

In the given figure, three resistances R1, R2 and R3 are connected ----V--_.
in parallel with a source of potential difference ‘V’. Let a current
‘I’ flows through the circuit. The current ‘I’ at point ‘A’ is divided Swit-ch-=d-n-~ +
into three currents as I1 along R1, I2 along R2 and I3 along R3.
fig:parallel connection of resistors
Now, from Ohm’s law, the individual current through each
resistor is given by

I1= V , I2= V , I3= V (since, I= V )
R1 R2 R3 R

These three currents recombine at point ‘B’ to give the same

current ‘I’. i.e., I = I1 + I2 + I3

If R be the equivalent resistance of the parallel connection, then

V = V + V + V
R R1 R2 R3

∴ 1 = 1 + 1 + 1
116 R R1 R2 R3

Optional Science - 10

PHYSICS

Characteristics of parallel connection of resistors

1. There is a separate conducting path for all resistors in a parallel circuit.

2. The potential difference across individual resistors is the same.

3. The current through different resistors is different. The total current I = I1 +I2 +I3.

4. The sum of the reciprocal of the resistance of individual loads is equal to the reciprocal
1 1 1 1
of the equivalent resistance. i.e., R = R1 + R2 + R3

Advantages of parallel connection

In parallel connections, each resistor or electric load has a separate circuit for the flow of
electricity. So

1. A separate switch can be used for an individual resistor. In a domestic circuit, electrical
appliances can be operated independently.

2. If one resistor stops working due to some defect, then all others keep working normally.

3. Each resistor gets the same voltage. For example in our domestic circuit, all appliances
have the potential difference of 220 V as that of the power supply line.

4. The overall resistance of the resistors gets reduced. Due to this, the current from the
power supply is high.

Know the Reason

In our domestic circuit, when one bulb burns out, the other bulbs in the circuit remain
lit, why?

Electric loads are connected in parallel in a domestic circuit. Each bulb has a separate
conducting path for current. So, in our domestic circuit, when one bulb burns out, the
other bulbs in the circuit remain lit.

Solved numerical- 6.

Resistors of 10Ω, 15Ω and 20Ω, are first connected in series and then in parallel. Calculate their
equivalent resistances in both the cases.

Solution: Here, Resistance of the first resistance (R1) = 10Ω
Resistance of the first resistance (R2) = 15Ω
Resistance of the first resistance (R3) = 20Ω
In a series circuit, the equivalent resistance is given by

R = R1 +R2 +R3Substituting the value of R1, R2 and R3
R = 10 + 15 + 20 = 35Ω,

In parallel circuit, the equivalent resistance is given by

1 = 1 + 1 + 1
R R1 R2 R3

Or 1 = 1 + 1 + 1 = 6+4+3 = 13
R 10 15 20 60 60

∴ R= 60 = 4.6 Ω
13

Optional Science - 10 117

PHYSICS

Diodes

A diode is a two terminal electric

component that allows electric current Generic Diode "' #
to flow in only one direction. One of its Schottky Diode
electrodes is positively charged whereas ~ Zener Diode /
the other is negatively charged. A diode
allows an electric current to pass in one
direction but blocks the current in the
opposite direction. So a diode can be

considered as a check valve in electronic LED Tunnel Diode Photo Diode

devices. Thermionic diodes were an early fig:Different types of diode

form of diode. Modern diodes are semiconductor diodes.

Thermionic diode/ vacuum tube diode

The method in which a metal is heated to a high temperature to make the Anode
free electrons in the metal gain kinetic energy sufficient to escape through its Heated
surface is called thermionic emission. The higher the temperature, the greater cathode
is the emission. Thermionic diodes are electron tubes in which electronic Heater
conduction occurs. It is also known as a vacuum tube diode. John Ambrose
Fleming invented the first true thermionic diode, the Fleming valve, in 1904. It fig:vacuum tube
consists of a sealed evacuated glass envelope containing two main parts. They diode
are the cathode and anode, or metal plate.

Semiconductor diodes

Most types of vacuum tube diodes have been replaced by semiconductor diodes. Semiconductor
diodes were the first semiconductor electronic devices. The first semiconductor diodes, called
cat’s whisker diode, was developed around 1906. A semiconductor diode is the most common
type of diode in use. Before you learn about the semiconductor diode, an introduction to the
semiconductor and its types is given here.

Semiconductor

A semiconductor is a solid substance that has conductivity between that of an insulator and
most metals. Such effect is either due to the addition of an impurity or because of temperature
effects. Silicon, germanium and selenium are the best known examples of semiconductors.
The electrical resistance of semiconductors lies in between the resistance of typical metals
and insulators. Devices made of semiconductors, notably silicon, are essential components of
most electronic circuits.

Types of semiconductors

Semiconductors can be classified into two types - intrinsic semiconductor and extrinsic
semiconductor - on the basis of their purity.

Semiconductor

f t

Intrinsic or pure semi-conductor Extrinsic or impur semiconductor

0118 P-Type e.g. Boron doped silicon N-Type e.g. Antimony doped silicon
Optional Science - 10
PHYSICS

Intrinsic Semiconductor: A semiconductor in it pure form is known as an intrinsic

semiconductor. For example, silicon and germanium crystals in their natural state are intrinsic

semiconductors. There are four valence electrons in the atoms of these semiconductors. In a

germanium crystal, each of the four valence electrons of every

atom are shared with electrons of neighboring atoms. There

are no free electrons. When some bonds break up due to

thermal agitation, then electrons are liberated. Along with the

formation of free electrons, there is formation of a vacant space

called the hole. These electrons and holes in an intrinsic

semiconductor are called intrinsic carriers. Thus the

conductivity of an intrinsic semiconductor is very low, and Sharing of electrons

they are not used practically as semiconductors. fig:intrinsic semiconductor

Extrinsic semiconductor: In order to increase conductivity, impurities are added to intrinsic
semiconductors. The process of adding impurities to pure semiconductors is called doping.
Such doped semiconductors are called extrinsic semiconductors. Impurity atoms are of two
types:

i. Pentavalent impurity atoms: Pentavalent impurity atoms have 5 electrons in their
valence shell. For example, phosphorous (P), antimony (Sb), arsenic (As) can be used as
pentavalent impurity elements in an intrinsic semiconductor.

ii. Trivalent impurity atoms: Trivalent impurity atoms have 3 electrons in their valence
shell. For example, boron (B), aluminium (Al), gallium (Ga) can be used as trivalent
impurity elements in an intrinsic semiconductor.

Types of Extrinsic Semiconductors

On the basis of the impurity atom added to an intrinsic semiconductor, there are two types of
extrinsic semiconductors: N-type semiconductor and P-type semiconductor.

N-type semiconductor

When a pentavalent impurity atom is added to an intrinsic semiconductor, then out of five
··•·
electrons, four electrons form a covalent bond with 4 valence \ • Donar Impurity

electrons of 4 atoms of silicon or germanium. Due to this, the • y Contributes Free
5th electron of the impurity atoms remains free to conduct
electricity. Therefore, negatively charged electrons are the ··• ·.. :e :: ::• :......·• ··.._~ectrons
charge carriers in N-type semiconductors. Thus, an extrinsic
• .. •. .• . . .. •· ··· .·.•:S::b.·•·.~ ·· ··
semiconductor, which is created by doping an intrinsic AntimonyAdded • ♦
. .semiconductor with a pentavalent impurity element like
as Impurity ..

·

phosphorous (P), in which electrons are the majority carriers fig:n-type semiconductor

and holes are the minority carriers, is called a N-type semiconductor. ··•··• •.. . . .··• ·· · . . ::o; :~ ~atesa Hole
• Acceptor Impurity
P-type semiconductor

When a trivalent impurity atom is added to an intrinsic
semiconductor, then three electrons form a covalent bond with

3 valence electrons with atoms of silicon or germanium. Due to •. •
this, one vacancy is created. Thus for every trivalent impurity ·
atom, an extra hole will be created. Therefore, positively ..•.. ..•..·
charged holes are the charge carriers in P-type semiconductors. • .·.• :B::.•·iii · •
Boron Added j
as Impurity ··

.•.•. •·· ·.

fig:p-type semiconductor

PHYSICS 0Optional Science - 10 119

The silicon or germanium crystal so obtained is called a P-type semiconductor. Each hole is
equivalent to a positive charge. Thus, an extrinsic semiconductor, which is created by doping
an intrinsic semiconductor with a trivalent impurity element like boron (B), in which holes are

the majority carriers and electrons are the minority carriers, is called a P-type semiconductor.

P-N junction diode

A PN junction diode is a two terminal device whose one side is made a P-type semiconductor
and another side an N-type semiconductor by doping on an intrinsic semiconductor. It is
formed by placing a P-type semiconductor crystal in contact with an N-type crystal and
subjecting it to a high pressure so that it becomes a single piece. The layer model and circuit
symbol of a P-N junction diode are shown in the given figure. In the case of a P-N junction
diode, conventional current flows from the P-type to the N-type segment of the diode. It is
against the direction of electron flow.

At the junction of the two types of semiconductors, there is diffusion of electrons and holes.
During diffusion, electrons are removed from the N-type semiconductor and holes are added.
Similarly, the P-type semiconductor loses its holes and acquires electrons. This continues till
n equilibrium is established at the junction. The region free from any charge carrier, which is
formed by the diffusion of electrons and holes at the junction of a P-N junction diode, is called
the depletion layer. Due to neutralization of the charge carriers at the junction, the P-section
of the junction becomes slightly negative while the N-section becomes slightly positive. The
potential difference thus developed across the junction is called a potential barrier. It stops
further neutralization of charge carriers. The potential barrier is approximately 0.5V to 0.7V
for silicon diodes and approximately 0.3 V for germanium diodes.

Forward biasing and reverse biasing of a junction diode

►A n o d e ICathode C atho de (K) An ode (A ) ~ Anode ►Anode l c a th : de

Schematic Symbol ..-~ + Cathode ---~
Convent ional Current Flow Open c ircuit
Stripe m a rks cathode conventional current flow ••

Re a l compo ne nt Closed c ircuit
appearance
Forward biased Reverse biased
P-N junction diode symbol with its terminals
forward biasing and reverse biasing

A junction diode can be biased in the following two ways:

1. Forward bias: When a battery is connected to the P-N junction diode with the P-section
connected to the positive terminal and N-section to the negative terminal, the diode is
said to be forward biased.

2. Reverse bias: When a battery is connected to the P-N junction diode with P-section
connected to the negative terminal and N-section to the positive terminal, the diode is
said to be forward biased.

Advantages of P-N junction diode over vacuum tube diodes

1. P-N junction diodes are very compact due to their small size.
2. They are cheaper than the cost of a vacuum tube.
3. They have very long life.
4. They are shock proof.

0120 Optional Science - 10

PHYSICS

Disadvantage of a semiconductor diode

The main disadvantage of a semiconductor diode is the possibility of its breakdown due to
rise in the temperature and on the application of high voltage.

Applications of diodes

1. Radio demodulation: The audio is extracted from the modulated radio signal by using
diodes.

2. Power conversion: The rectifiers which convert alternating current (AC) into direct
current (DC) are constructed from diodes.

3. Over-voltage protection: Diodes are used for protection from over-voltages at high
power.

4. Temperature measurement: The forward voltage drop across a diode depends on the
temperature. So a diode can be used as a temperature measuring device.

5. Uninterrupted power supply (UPS): A diode can be used in an UPS to ensure that
current is only drawn from the battery when necessary.

Transistor

The transistor moved the world from power-hungry vacuum tubes to portable solid-state
electronics. Vacuum tubes were the basic components of electronic devices throughout the
first half of the 20th century. They were used in the advancement of the radio, television, radar,
sound amplification, sound recording and reproduction, large telephone networks, analog
and digital computers, and industrial process control. Invention of the vacuum tube made
these technologies widespread and practical.

In the 1940s, the invention of semiconductor devices made it possible to produce solid-
state devices. The first practically implemented semiconductor device was a point-contact
transistor invented in 1947 by American physicists John Bardeen, Walter Brattain and William
Shockley. Such devices are smaller, more efficient, more reliable, more durable and cheaper
than vacuum tubes. From the mid-1950s, solid-state devices, such as transistors, gradually
replaced the tubes. However, there are still a few applications for which vacuum tubes are
preferred to semiconductors, for example, the magnetron used in microwave ovens, and
certain high-frequency amplifiers.

A transistor is a semiconducting device equivalent to a triode valve. A transistor is a three
terminal semiconductor electronic device with a P-type or N-type semiconductor region
sandwiched in such a way that there is formation of two P-N junctions. Transistors are widely
used to amplify electronic signals and switch electrical power.

Construction

In a P-N junction diode, there are two doped elements, namely the P-type semiconductor and
N-type semiconductor. A transistor is formed when a third doped element, either a P-type
semiconductor or N-type semiconductor, is added to a P-N junction diode in such a way that
there is formation of two P-N junctions. Thus a transistor is made by the following two ways:

i. Sandwiching a P-type semiconductor between a pair of N-type semiconductors.

ii. Sandwiching a N-type semiconductor between a pair of P-type semiconductors.

Optional Science - 10 121

PHYSICS

Three sections of a transistor

Emitter, base and collector are the three sections of a transistor. All these three regions are
provided with terminals which are labeled E (for emitter), B (for base) and C (for collector)
respectively. A brief description of these terminals is given in the following points:

i. Emitter (E): The section on one side that supplies the Emitter~ e c t o r

charge carriers, which are either electrons or holes,

lis called the emitter. The emitter is thinner than the
Ba ■ e _ .,

Emitter~ l e c t o r

collector, but much thicker than the base. It is heavily l Base
doped. In a circuit, it is denoted by E or e.
three regions in NPN and PNP transistors
The emitter is always forward biased with respect to

the base. In the given figure, the P-type emitter of the

transistor is forward biased. It supplies holes to its

junction with the base. In the second figure, N-type

emitter of the transistor is forward biased. It supplies

free electrons to its junction with the base.

Function of emitter: Its main function is to supply symbol of NPN symbol of PNP
majority charge carriers to other regions. transistor transistor

Know the Reason

The emitter of a transistor is heavily doped, why?
The emitter is heavily doped and always forward biased with respect to the base so that
it can supply a large number of majority carriers.

ii. Base (B): The base is the middle region of a transistor. It is the thinnest region and
lightly doped. It is equivalent to the grid in a triode as it performs a function similar to
it. The emitter-base is always forward biased while collector-base is reverse biased. In a
circuit it is denoted by B or b.

Function of base: Its main function is to pass the majority charge carriers injected from
the emitter on to the collector.

Know the Reason

The base of a transistor is lightly doped, why?
Some electrons and holes combine in the base region. So the base of a transistor is lightly
doped to minimize the recombination of electrons and holes.

iii. Collector (C): The collector is situated on the other side of the emitter on a transistor. It
is the thickest region. It is a moderately doped region. The collector is made thick so as
to dissipate the heat produced in the collector circuit. In a circuit, it is denoted by C.

Function of collector: The main function is to collect the majority charge carrier supplied
by the emitter and passed by the base.

122 Optional Science - 10

PHYSICS

Application of transistors
Transistors are employed in approximately all digital circuits. Common applications of a
transistor are seen in analog and digital switches, power regulators, signal amplifiers and
equipment controllers. Microprocessors over and over again comprise more than a billion of
transistors in every single chip. Switching and amplification are the two types of applications
of a transistor.

Transistor as a switch: In transistors, current flows in collectors only when current flows in
the base circuit. This property is applicable while using a transistor as a switch.

a. In a light-operated switch, the transistor is used to design a circuit to light the bulb in a
bright environment and to turn it off in the dark.

b. It is used in a circuit of a heat-operated switch along with a thermistor as in a fire alarm.

c. In digital electronics, it is used as a high speed electronic switch as in an Integrated
Circuit (IC).

Transistor as an amplifier

a. Transistors are used in many electronic devices to amplify current as in microphones.

b. In a communication system, it is used as the primary component in an amplifier.

Answer writing skill I

1. What is a step-up transformer?
A transformer which converts the applied low voltage AC to high voltage AC is called a
step-up transforer.

2. Mention an important feature of a DC generator.

In a DC generator, two ends of the coil are connected to two copper half rings, or split
rings, R1 and R2 of a commutator.

3. Write four differences between a diamagnetic substance and a paramagnetic substance.

Diamagnetic substance Paramagnetic substance

A diamagnetic substance is feebly repelled A paramagnetic substance is feebly

by a magnet. attracted by a magnet.

In a non-uniform magnetic field, the In a non-uniform magnetic field, the

diamagnetic substance is repelled towards paramagnetic substance is attracted

the weaker part of the field. towards the stronger part of the field.

The permeability is less than one but can The permeability is slightly greater than

never be negative. one.

The intensity of magnetization (I) has a The intensity of magnetization (I) has a

small negative value for a diamagnetic small positive value for a paramagnetic

substance. substance.

PHYSICS 0Optional Science - 10 123

4. Mention the effect on a freely suspended rod of diamagnetic, paramagnetic and

ferromagnetic material in a magnetic field.

a. A diamagnetic rod freely suspended in a uniform magnetic field, slowly turns to
set at right angle to the applied magnetic field

b. When a rod of paramagnetic substance is freely suspended, in a magnetic field, it
aligns along the field.

c. When a rod of a ferromagnetic substance is freely suspended in a uniform
magnetic field, it rotates and aligns itself parallel to the field.

5. The p.d. of the power supply to the primary coil of a transformer is 220 V and the
turns in the primary coil are 2000. What must be the number of turns in the secondary
coil to run a radio of 11 V from the transformer?

Solution

Here, Primary voltage (V1 ) = 220 V
Secondary voltage (V2 ) = 11V
Primary turns ( n1) = 2000
Secondary turns ( n2) = ?
Now,

The number of secondary turns is given by the formula

Secondary voltage (V2) = Secondary turns (n2)
Primary voltage (V1) Primary turns (n1)

Or, n2 = V2 × n1 = 2000× 11 = 100 V
V1 220

The number of turns in the secondary coil must be 100.

6. Explain the operating principle of a transformer. Also mention the reason of why a
transformer does not work with DC.

Alternating current passes through the primary coil when it is connected to an AC
source. Hence, a magnetic field is produced by the primary coil. The magnetic field
due to A.C. in primary coil changes in both magnitude and direction. This changing
magnetic field changes the magnetic lines of force linked with the secondary coil.
According to the faradays laws of electromagnetic induction, whenever the magnetic
lines of force linked with a closed circuit changes, an e.m.f. gets induced from two
terminals of the secondary coil. Thus, the induced current is also an alternating current.
Instead of AC, if DC is supplied in the primary coil then the magnetic field produced is
of constant strength. The number of magnetic lines of force which are intersected by the
secondary coil does not change. In such condition current does not get induced from the
two terminals of secondary coil. Thus, transformer does not work with DC.

0124 Optional Science - 10

PHYSICS

Exercise

1Step 2. Magnetic permeability 3. Magnetic susceptibility
5. Paramagnetic material 6. Ferromagnetic material
Define 8. Fleming’s right hand rule 9. Primary voltage
1. Magnetization 11. Secondary coil 12. Secondary voltage
4. Diamagnetic material
7. Magnetic flux
10. Primary coil

Very short answer questions

1. Give four examples each of b. paramagnetic materials
a. diamagnetic materials

c. ferromagnetic materials
2. Name two of the strongest diamagnetic materials
3. What is electromagnetic induction?

4. Name the two devices which are based on

a. electromagnetic induction b. motor effect
5. What is a bicycle dynamo?

6. What is an electric generator?

7. What is meant by magnetic effect of current?

8. Name the scientist who discovered

a. the magnetic effect of current b. electromagnetic induction
9. What is an electric motor?

10. Name the main elements in:

a. AC generator b. DC generator

11. What is a transformer?

12. Name the two types of transformers on the basis of number of windings.

Optional Science - 10 125

PHYSICS

13. Write the working principle of the

a. generator b. electric motor

c. transformer
14. What is a resistor?

15. Give two ways to connect resistors in a circuit.

16. What is a diode?

17. Name the electrodes used in a diode.

18. What is a transistor?

2Step

Short answer questions

1. State molecular theory of magnetism.

3. ‘Frequency of the power supply in a domestic circuit is 50 Hz’. What does it mean?

4. Write the Faraday’s three laws of electromagnetic induction.

5. What change occurs in the brightness of a bulb connected to a bicycle dynamo when the
wheel’s speed of rotation increases?

6. Mention the factors on which the strength of the induced current depends?

7. Write four methods to increase the strength of the current generated from a dynamo or
generator.

8. Make a comparison between DC motor and DC generator in two points.

9. Mention four characteristics each of

a. Series connection of resistors b. Parallel connection of resistors

10. Write two advantages and two disadvantages each of

a. Series connection of resistors b. Parallel connection of resistors

11. What do the three fingers, namely thumb, fore finger and middle finger indicate in
Fleming’s right hand rule

12. Write two applications each of the

a. electric generator b. electric motor
c. Diode. d. transistors

e. step-up transformer f. step-down transformer

13. Write the two laws in which a transformer is based on.

14. ‘Use of alternating current would be limited in the absence of a transformer’. Justify this
statement.

15. Write in short about the following three sections of a transistor with their function

a. Emitter (E) b. Base (B)

c. Collector (C)

0126 Optional Science - 10

PHYSICS

Differentiate between
1. AC and DC
2. Electric generator and electric motor
3. AC generator and DC generators
4. AC motor and DC motor
5. Step-up transformer and step-down transformer
6. Series connection of resistors and parallel connection of resistors
7. Intrinsic semiconductor and extrinsic semiconductor

8. N-type semiconductor and P-type semiconductor

Give reason
1. In a series connection and parallel connection, the parallel connection of resistors

decreases the total resistance of the circuit.

2. A stationary magnet does not induce a current in a coil.
3. The core of a transformer is laminated.
4. The number of turns in the primary coil and secondary coil of a transformer is different.
5. Transformer does not alter the voltage of direct current (DC).
6. In our domestic circuit, when one bulb burns out, the other bulbs in the circuit remain

lit.
7. A diode is called a valve in an electronic circuit.
8. A vacuum tube diode blocks the negative half cycle of AC
9. The emitter of a transistor is heavily doped.

10. The base of a transistor is lightly doped.

Answer the questions with the help of the given figure

1. In the given figure, a copper wire is being moved perpendicular to the magnetic lines of
force in the U-shaped magnet. Two ends of a wire are connected in Galvanometer.

a Why does the Galvanometer show deflection due to the
movement of the wire?

b. Write any two ways that the deflection of the Galvanometer
can be increased.

c. What will happen when the Galvanometer is replaced by
a battery? What is the effect called?

Laminated Iron Core

2. Which type of transformer is given in the picture? 220 V 100turns
b. Write any one application.
c. Calculate the voltage produced in the secondary coil. 1000 turns

[Ans: 22 V]

PHYSICS 0Optional Science - 10 127

3. Which effects are shown in the given figure ‘a’ and ‘b’? Write any two applications of

each. -<E------ current
direction

magnetic
fields in
-<E-------the same
direction

repel

wire pushed wire
in this
a
direction

b

3Step

Numerical problems

1. A transformer of 1000 primary turns is connected to a 220 V AC supply. How many turns
of the secondary coil will be needed in order to generate 110 V from that transformer?
[Ans: 500 ]

2. The power supply is of 240 V and the number of turns in the primary coil of a transformer

is 1000. What should be the number of secondary turns to generate an output of 12V, 24

V and 120 V? [Ans: 50, 100, 500 turns]

3. A transformer has 600 turns of wire in the primary coil and 1200 turns of wire in the

secondary coil. The potential difference across the primary coil is 110 V. What is the

potential difference induced across the secondary coil? [Ans: 220 V]

4. The number of turns in the primary and secondary coils of a transformer is 1200 and 300
respectively. If secondary voltage is 55 V, then, calculate its primary voltage.[Ans: 220 V]

5. In a transformer the secondary turns are 4 times more than the primary turns. What
should be the input voltage in the transformer to obtain an output of 220 V?
[Ans: 55 turns]

6. In a transformer, the ratio of secondary turns to primary turns is 2:3. Which type of

transformer is it? Find the secondary voltage when the transformer is connected to a

power supply of 220 V. [Ans: 146.667 V]

7. An input voltage and output voltage in a transformer are 12 V and 220 V respectively.
What is the current in the primary coil when the output current is 0.75 A?[Ans: 13.75 A]

8. A step-up transformer has 5,000 turns on its secondary coil and 100 turns on its primary
coil. An alternating current of 5 A flows in the primary coil when it is connected to a 12
V AC supply. Calculate

1. The power input to the transformer
2. The emf induced across the secondary coil.
3. Current in the secondary coil.

[Ans: 60 W, 600V, 0.1 A]

128 Optional Science - 10

PHYSICS

Draw a diagram

1. Draw a diagram to show the pattern of magnetic lines of force when

a. a diamagnetic material is placed within a magnetic field
b. a paramagnetic material is placed within a magnetic field
c. a ferromagnetic material is placed within a magnetic field
3. Draw a diagram to show the magnetic field around a straight current carrying wire.

4. Draw a diagram to show electromagnetic induction.

5. Draw a labeled diagram to show the construction of a bicycle dynamo.

6. Draw a diagram to show the current time relation in the case of

a. alternating current b. direct current

7. Draw a diagram to show the construction of

a. AC generator b. DC generator

8. Draw a diagram to show the direction of three fingers and their corresponding indication in
Fleming’s right hand rule

9. Draw a labeled diagram to show the construction of a step-up transformer and step-
down transformer.

10. Draw a labelled diagram and corresponding symbol of P-N junction diode.

4Step

1. Explain the main characteristics of

a. diamagnetic substance b. paramagnetic substance

c. ferromagnetic substance

2. Mention the main characteristics of a paramagnetic substance which are opposite of

diamagnetic substances.

3. Make a comparative study of ferromagnetic substances with paramagnetic substances
and diamagnetic substances.

4. Explain an experiment to demonstrate electromagnetic induction.

5. Describe the construction and working of the following:

a. Bicycle dynamo b. AC generator. c. DC generator

d. DC motor e. transformer

6. Explain the role of the transformer in changing the voltage of an alternating current.

PHYSICS 0Optional Science - 10 129

Multiple choice question [MCQ]

1. The magnetic substances which are strongly attracted by a magnet are

a. diamagnetic substance b. ferromagnetic substance

c. paramagnetic substance d. none of above

2. Frequency of AC in our domestic circuit is

a. 50 Hz b. 60 Hz

c. 240 Hz d. 220 Hz
3. Bicycle dynamo converts

a. mechanical energy into magnetic energy.

b. electrical energy into magnetic energy.

c. mechanical energy into electrical energy.

d. electrical energy into mechanical energy
4. Principle of dynamo is

a. electromagnetic induction b. motor effect

c. Ohm’s law d. mutual induction

5. The primary coil of a step-down transformer has:

a. less number of turn b. more number of turns

c. very less e. all of the above

6. The transformer formula is

a. V1 = n2 b. V2 = v1
V2 n1 n1 n2

c. V2 = n1 d. V2 = n2
V1 n2 V1 n1

Project Work

1. Make a model of DC generator: Buy a DC electric motor. Connect a small low power LED
bulb to two terminals of the connecting wires. Now rotate the shaft of the motor by
your hand. Do you observe the bulb glowing with changing brightness? What happens
to the brightness of the bulb when you rotate it faster? Discuss in your group to draw a
conclusion.

2. Visit an electric workshop and request the motor repair person to show you the parts of a
DC and AC motor. Observe their parts and note them. Finally note their working method
and present your study in the class.

130 Optional Science - 10

PHYSICS

UNIT ATOMIC
STRUCTURE
7

About the inspiring personality: John Dalton born in September 6, 1766, in Eagles field,
England. He died on July 26, 1844 in Manchester, England. He was the greatest scientist
in his time. The modern atomic theory was first formulated by John Dalton. So, he is well
known from the Dlalton atomic theory. The sex-linked disease, viz. colour-blindness was first
studied by John Dalton. John Dalton also proposed a concept of Partial Pressures in 1803,

which is known as Dalton’s Law of Partial pressure.

Syllabus issued by CDC Learning objectives:

Theory 6 At the end of this unit, the students will be able to:
Practical 2
• Explain atomic mass, molecular mass and
mole concept.

• Atomic mass, molecular mass and • Explain Avogadro’s number and Quantum

mole concept number.

• Quantum numbers • Describe normality, molality, molarity,

• Concentration (Normality, grams per litre and percentage along with
the calculation of these quantities in some
molarity, gram per litre and chemical compounds.

percentage)

Key terms and terminologies of the unit

1. Atom: An atom is the smallest particle of an element which can neither be created
nor be destroyed and involves in chemical reaction without division.

2. Atomic mass: The total mass of protons and neutrons which are present in the
nucleus of an atom is called atomic mass.

3. Amu: Amu is a unit of mass which is used to measure the mass of very small
particles like atoms, electrons, protons, neutrons, etc. It is equal to the mass of
1/12th of mass of carbon-12 isotope.

4. Molecular formula: The symbolic representation of one molecule of a substance
is called molecular formula.

Optional Science - 10 131

CHEMISTRY

5. Molecular mass: The sum of atomic mass of all atoms present in a molecule is
6. called molecular mass.
7. One mole: The amount of substance which contains 6.022 × 1023 atoms, ions,
8. molecules or even sub-atomic particles is called one mole.
9. Molar mass: The total amount of mass present in one mole of a pure substance is
10. called molar mass. Its SI unit is gram per mol.
11. Avogadro’s Number: Avogadro’s Number is the number of atoms, molecules,
12. ions or particles present in one mole of a pure substance. It is equal to 6.022 × 1023.
13. Orbital: The region around the nucleus where there is high probability of finding
14. the electrons is called orbital.
15. Quantum number: The characteristics of an electron and its position are
16. determined by a set of specific number called quantum number.
17. Principal quantum number: Principal quantum number represents the main
energy level or shell to which the electrons belong to.
18. Azimuthal quantum number: Azimuthal quantum number describes the angular
momentum of an electron and shape of the orbital or sub-shell.
19. Magnetic quantum number: Magnetic quantum number is the third set of
20. quantum number which describes the orientation of the sub-shells.
21. Solution: The homogeneous mixture of solute and solvent is called solution.
22. Concentration: The amount of solute dissolved in a given amount of solvent is
23. called concentration.
24. Percentage by mass: The amount of solute present in 100 g of solution is called
25. percentage by mass.
26. Percentage by volume: When the amount of dissolved solute is measured in gram
(g) and the amount of solution is measured in 100 millilitres (mL), it is called
0132 percentage by volume.
Percentage by volume: When the amount of dissolved solute is measured in mL
and prepared solution is measured in 100 millilitres (mL), it is called percentage
by volume.
Grams per litre: The mass of solute in gram present in one litre of solution is called
grams per litre.
Molarity: Molarity (M) is the number of moles of solute present in one litre of
solution.
Molar solution: The solution containing one mole of solute in one litre solution is
called molar solution.
Decimolar solution: If a solution contains 1/10 mole of a solute in one litre solution,
then it is called decimolar solution.
Molality (m): The number of moles of solute present in one kilogram of solvent is
called molality (m).
Normality (N): The number of equivalents of a solute present in one litre of
solution is called normality (N).
Normal solution: The solution containing one equivalent of solute in one litre of
solution is called normal solution.
Decinormal solution: The solution containing 1/10 equivalent of solute in one litre
of solution is called decinormal solution.

Optional Science - 10

CHEMISTRY

Introduction

There are different kinds of matter around us. Examples: soil, rock, book, pen, pencil, clothes,
medicine, etc. Among them some are natural and some are man-made, some are pure and
some are impure. The elements and compounds are pure matter and others are impure matter.
Elements are made up of atoms and compounds are made up of molecules. Atoms are the
smallest particles of elements. They can neither be created nor be destroyed. They involve in
chemical reaction without division. They are the building blocks of matter. They are the same
as bricks of a building. Thus, atom is the smallest particle of an element which can neither be
created nor be destroyed and involves in chemical reaction without division. The word atom
is derived from the Greek word “atomus”, it means indivisible particle. So, atoms cannot be
broken down into further simpler substances. All the atoms of an element are the same in all
aspects but atoms of different elements are different with each other. An atom is made up
of mainly three types of small particles called sub-atomic particles or fundamental particles.
They are electrons, protons and neutrons. In the structure of an atom, about 99% of an atom is
made up of empty space. The remaining 1% is made up of sub-atomic particles. So, the main
part of an atom is concentrated into a very small volume.

Memory Plus

In the structure of an atom there are two parts. They are shells and nucleus. Shells occupy
about 99% of the total volume and nucleus occupies only about 1%.

Atomic mass or atomic weight

In an atom, there are electrons, protons and neutrons. To calculate the total mass of an atom, the
mass of electrons, protons and neutrons should be added. So, atomic mass is the calculation
of the total mass of an atom. The protons and neutrons have about equal mass. But the mass
of an electron is very less. The mass of electron is about 1837 times smaller than a proton.
Therefore, the mass of an electron can be neglected while calculating the total mass of an atom.
It means that the mass of an atom is the sum of mass of protons and neutrons.

Actually, mass and weight are different things. Mass is the total amount of matter present in
a body. Its SI unit is kg. While weight is the amount of force applied by the earth to pull the
body. Its SI unit is newton (N). The bigger object has more mass and more weight. Similarly,
the smaller object has less mass and less weight. But for the smaller particles like the sub-
atomic particles of an atom, viz. electrons, protons and neutrons, the mass and weight are
conventionally the same thing.

The total mass of protons and neutrons which are present in the nucleus of an atom is called

atomic mass. Generally, it is also called atomic weight. Atomic weight is usually measured in

atomic mass unit (amu). The mass of one proton or one neutron is equal to one amu. Therefore,

if an atom has six protons and six neutrons, then the atomic mass will be 12 amu. Amu is a

unit of mass which is used to measure the mass of very small particles, like protons, neutrons,

electrons or atoms. While calculating the mass of an atom, we count the total number of

protons and neutrons of an atom and calculate the total mass of that atom. In kilogram, the

mass of one proton or one neutron is nearly equal to 1.67 × 10-27 kg. This mass is equal to ¹/1₂th

of mass of a carbon-12 isotope. This is also called atomic mass unit (amu). Thus, amu is a unit

of mass which is used to measure the mass of very small particles like protons, neutrons,

electrons or atoms. It is equal to the mass of ¹/1₂ ᵗh of mass of carbon-12 isotope.

CHEMISTRY 0Optional Science - 10 133

Take an example of oxygen atom. In this atom, there are eight protons and eight neutrons
in its nucleus. After adding, the total number of protons and neutrons, it becomes sixteen.
Therefore, the mass of one oxygen atom is 16 amu. To express atomic mass of oxygen in
kilogram, it is necessary to multiply sixteen with 1.67× 10-27 kg.

Example: 1

Express atomic mass of hydrogen (1H1), sodium (11Na23), chlorine (17Cl35) and potassium
(19K39) in amu.

Solution:

For hydrogen, atomic mass = p + n

= 1+ 0 = 1 amu

For sodium, atomic mass = p + n

= 11 + 12 = 23 amu

For chlorine, atomic mass = p + n

= 17 + 18 = 35 amu

For potassium, atomic mass = p + n

= 19 + 20 = 39 amu

Molecular mass or molecular weight

Molecules are the smallest particle of a compound. They can exist independently. They show
all the properties of the compound. They are represented using formula. Examples: water
(H2O), sodium chloride (NaCl), calcium carbonate (CaCO3), sulphuric acid (H2SO4), glucose
(C6H12O6), etc. Thus, the symbolic representation of one molecule of a substance is called
molecular formula. Molecules may be monoatomic, diatomic, triatomic or polyatomic. In case
of monoatomic molecules like helium, neon, argon, krypton, xenon and radon the formula for
atom and molecule is the same. The atomic mass and molecular mass for these inert gases is
also same.

Fact with reason

Inert gases are called monoatomic molecules. Why?

The atoms of inert gases like helium, neon, argon, krypton, xenon, radon, etc. can exist
independently. They do not combine with other atoms. So, atoms of these elements are
called monoatomic molecules.

In case of diatomic, triatomic and poly atomic molecules, the molecular mass is calculated

by adding the atomic mass of all atoms of the molecule. For this, it is necessary to calculate

total number of atoms of different elements present in the molecule. As we have already

discussed that the mass of an atom can be calculated by adding the total number of protons

and neutrons present in the nucleus of that atom. The same concept can also be used to

calculate the molecular mass of a compound. To illustrate above concept, let us take a

methane molecule (CH4). This molecule has one carbon atom and four hydrogen atoms. So,
the total mass of methane is equal to the mass of one carbon atom and four hydrogen atoms.

0134 Optional Science - 10

CHEMISTRY

The atomic mass of carbon atom is 12 and hydrogen atom is 1. Therefore, the total mass of
methane molecule is 12 + 4 or 16 amu. Similarly, the mass of carbon dioxide (CO2) is equal to
1 × mass of carbon atom + 2 × mass of oxygen atoms. It is equal to 1×12 + 2×16 amu or 44 amu.
From the above discussion it is clear that, the sum of atomic mass of all atoms present in a
molecule is called molecular mass. For example, the molecular mass of hydrogen molecule is 2
amu. It means that hydrogen molecule is 2 times heavier than ¹/1₂th mass of carbon-12 isotope.
Similarly, the molecular mass of sulphuric acid is 98 amu. It means that, sulphuric acid is 98
times heavier than the ¹/1₂th mass of carbon-12 isotope.

Fact with reason

The molecular mass of oxygen molecule is 32 amu. What does it mean?

The molecular mass of oxygen molecule is 32 amu. It means that, the sum of atomic mass
of oxygen molecule is 32 or it is 32 times heavier than 1/12th mass of carbon-12 isotope.

Example: 2

Calculate molecular mass of calcium sulphate (CaSO4).

Molecular mass of CaSO4 = 1×Ca + 1×S + 4×O

= 1×40 + 1×32 + 4×16

= 40+32+64

= 136 amu

Example: 3

Calculate molecular mass of calcium carbonate (CaCO3).

Molecular mass of CaCO3 = 1×Ca + 1×C + 3×O

= 1×40 + 1×12 + 3×16

= 100 amu

Example: 4

Calculate molecular mass of ammonium sulphate (NH4)2SO4
Molecular mass of (NH4)2SO4 = 2×N + 8×H + 1×S + 4×O

= 2×14 + 8×1 + 1×32 + 4×16

= 28 + 8 + 32 + 64

= 132 amu

Mole Concept

In our daily life, we use to buy and sell different things in terms of number or in terms of
mass (or weight) or in terms of volume. For example, we buy pen, pencil, book, exercise book,
biscuits, eggs, banana, etc. in terms of number and we buy sugar, rice, wheat, etc. in terms of
mass (or weight). Similarly, we buy different liquids like milk, oil, etc. in terms of volume.
To measure different quantities we use different kinds of measuring units such as kilogram,
gram, milligram, litre, millilitres, etc. It is not possible to count the numbers everywhere. For
example, we cannot count the number of wheat and rice grains while buying from the shop.
Similarly, atoms, molecules, ions, etc. are so small particles that we cannot count. So, chemistry
introduced "mole" to measure these quantities.

Optional Science - 10 135

CHEMISTRY

In chemical reaction, fixed numbers of atoms or molecules or ions react to given a fixed amount
of products. For example, two molecules of hydrogen and one molecule of oxygen react together
to given two molecules of water. If we take only one molecule of hydrogen and one molecule of
oxygen, it does not give water. But it is very difficult to count the number of atoms or molecules
during the chemical reaction. This is because a small quantity of mater contains a large number
of particles or atoms or molecules or ions. To solve this problem, the mole concept has been
introduced. It is used to measure how much of a substance is present in a given sample. For a
reference of measurement we have chosen carbon-12 isotope. One mole of a substance contains
as many atoms or molecules or ions as there are in 0.012 kilogram or 12 grams of carbon-12
isotope. It has been calculated that, in 0.012 kilogram or 12 grams of carbon-12 isotope there are
6.022 × 1023 atoms. It is called one mole of carbon. Therefore, mole is a collection of very small
particles that includes atoms, ions, molecules or even sub-atomic particles like electrons, protons
and neutrons. The amount of substance which contains 6.022 × 1023 atoms, ions, molecules or
even sub-atomic particles is called one mole. The symbol of mole is "mol".

To understand the mole concept, let us consider an atom of oxygen, a molecule of oxygen, a
molecule of carbon dioxide and an ion of oxygen. According to atomic mass and molecular
mass, one atom of oxygen has 16 amu, one molecule of oxygen has 32 amu, one molecule of
carbon dioxide has 44 amu and one oxygen ion has 16 amu. Now, if we take one gram molecular
weight of these substances then we have 16 grams of oxygen atom, 32 grams of oxygen molecule,
44 grams of carbon dioxide and 16 grams of oxygen ion. The amount of matter present in these
substances (atom, molecule and ion) is called one mol. It can be further clarified as:

1. 16 gram of oxygen atom is also called one mole of oxygen atom.
2. 32 grams of oxygen molecule is also called one mole of oxygen molecule.
3. 44 grams of carbon dioxide molecule is also called one mole of carbon dioxide.
4. 16 gram of oxygen ion is also called one mole of oxygen ion.

Substances Symbol Mass in mass in mass in Number of
amu gram mole particles
Oxygen atom O
Oxygen molecule O2 16 16 1 6.022 x 1023
Carbon dioxide molecule CO2 32 32 1 6.022 x 1023
Oxygen ion O-2 1 6.022 x 1023
44 44 1 6.022 x 1023
16 16

The total amount of mass present in one mole of a pure substance is called molar mass. Its SI
unit is gram per mol.

Avogadro’s Number

As we know that Avogadro’s Number is the number of atoms, molecules, ions or particles
present in one mole of a pure substance. It is equal to 6.022 × 1023. The word Avogadro is
named after the honour of an Italian chemist Amedeo Avogadro who discovered this concept.
According to this concept one mole of a pure substance contains exactly equal number of
atoms or molecules or ions or sub-atomic particles which is numerically 6.022×1023. Now, the
number 6.022 × 1023 is called Avogadro’s number. It is denoted by a symbol (N0).

0136 Optional Science - 10

CHEMISTRY

Memory Plus

i. Number of atoms in 14 grams of nitrogen atom (N) = Number of molecules in 28

grams of nitrogen molecule (N2) = Number of molecules in 17 grams of ammonia
molecule (NH3) = Number of ions in 14 grams of nitrogen ion (N-3).

ii. Number of molecules = Mass of substance (m)× Avogadro's number
Molar mass (M)

Example: 1

Calculate the molar mass of KNO3 and find the number of molecules present in 5 mole of
KNO3.

Solution:

The molecular mass of KNO3 = 39 + 14 + 3 × 16 = 101 amu
Therefore, molar mass of KNO3 = mass of 1 mol of KNO3 = 101 gm/mole
The number of molecules in 1 mole of AgNO3 = Avogadro’s number = 6.022 × 1023 molecules
Hence, the number of molecules in 5 mole of KNO3 = 5 × 6.022 x 1023 = 30.31× 1023 molecules

Example: 2

Calculate the number of molecules present in 1 kg of carbon dioxide.

Solution:

1 kg of carbon dioxide = 1000 gram

As we know, 1 mole of carbon dioxide = 44 gram

= 6.022× 1023 molecules
6.22 × 1023
1 gram of carbon dioxide = 44 molecules

So, 1000 gram of carbon dioxide = 6.22 × 1023 × 1000 molecules
44

=136.86 × 1023 molecules

=1.3686 × 1025 molecules

Example: 3

Calculate the total number of carbon atoms and hydrogen atoms present in 1 kg of methane
(CH4).
Solution:

1 kg of methane = 1000 gram

As we know,

1 mole of methane = 16 gram = 6.022 × 1023 molecules

16 grams of methane = 6.022× 1023 molecules = 6.022× 1023 carbon atoms
So, 1000 gram of methane 6.22 × 1023
= 16 × 1000 carbon atoms

= 376.375 × 1023 carbon atoms

= 3.76 × 1025 carbon atoms 0Optional Science - 10 137

CHEMISTRY

Similarly, 1 mole of methane (CH4) = 16 gram = 6.022 × 1023 molecules = 4 × 6.022 × 1023
hydrogen atoms.

So, 1000 gram of methane = 4 × 6.22 × 1023 × 1000 hydrogen atoms
16

= 1505.5 × 1023 hydrogen atoms

= 1.5 × 1026 hydrogen atoms

Quantum number

We use a detail address to send a letter for a particular person. For example, Alish Panthi,
Madane Village Politian -7, Bhanbhane, Chaurapata, Gulmi. In this address, it is easy to find
Mr. Alish Panthi. Similarly, to find the position and energy of an electron, we need some
special numbers called quantum number. According to Bohr’s model of atomic structure, an
electron lies at a fixed distance from the nucleus. It is believed that an electron revolves around
the nucleus from this distance. But, this concept is rejected by the quantum mechanical model
of an atom. According to quantum mechanical model, an electron can be anywhere within
a certain region around an atom and its position cannot be accurately predicted. The actual
position and velocity of an electron cannot be calculated at the same time. It is believed that
electron is present anywhere around the nucleus. Thus, the region around the nucleus where
there is high probability of finding the electrons is called orbital. There are four major types of
orbitals. They are s-orbital, p-orbital, d-orbital and f-orbital. But, knowing only these orbitals
is not sufficient to study about the position and energy of an electron. Every electron has a
certain amount of energy. So, it is located at a certain position around the nucleus. It also
spins in its own axis in a particular direction. These properties of an electron are studied by
using a set of numbers called quantum numbers. Thus, the characteristics of an electron and
its position are determined by a set of specific numbers called quantum numbers. Quantum
numbers are used to decide the position, angular momentum, orientation and spinning
property of an electron. There are four quantum numbers. They are:

1. Principal quantum number (n)

2. Azimuthal (or Angular momentum) quantum number (l)

3. Magnetic quantum number (m)

4. Spin quantum number (s)

The principal quantum number (n)

The principal quantum number represents the main energy level or shell to which the electrons

belong to. It decides the size of the shell and the average distance of the shell from the nucleus.

The principal quantum number is denoted by the symbol "n". It has non-zero values like 1,2,3,

4, etc. It is also called energy level or shell number. These numbers also give idea about the

comparison distance of the orbitals from the nucleus. For example, the principal quantum

number n = 3 lies at a greater distance from the nucleus than the number n = 2. Meanwhile,

n = 3 is at a greater distance, it forms a bigger region of the circle than n = 2. From the above

example, it is clear that the size of shell having higher value of quantum number is bigger than

the shell having lower value of quantum number. The letters K, L, M, N, etc. are also used to

decide the energy level or shells. The maximum number of electrons present in each shell is

calculated by using 2n2 formula. For example,

0138 Optional Science - 10

CHEMISTRY

Principal quantum number (n) 1 2 3
Letter symbol K L M
Maximum number of electrons (2n2) 2 8 18

The azimuthal quantum number (l)

Azimuthal quantum number describes the Azimuthal quantum Sub-shells
angular momentum of an electron and shape of number (l)
the orbital or sub-shell. It also describes electrons
cloud around the nucleus. It is symbolized by the 0s
letter "l". For the given value of principal quantum
1p

number, the value of azimuthal quantum number 2 d

may have all integral values from 0 to n-1 like 0, 3 f

1, 2, 3……. (n-1). These numbers refer to the sub-

shells s, p, d and f for the numbers 0, 1, 2 and 3 respectively. The value of azimuthal quantum

number is upto one less than the principal quantum number along with zero. For example,

(1) For principal quantum number (n) = 1, the azimuthal quantum number (l) = 0. It
represents s-orbital which is spherical in shape.

(2) For n = 2, the value of l = 0 and 1. Here, the value 0 represents s-orbital and value 1
represents p-orbital.

(3) Similarly, for n = 3, the value of l = 0, 1 and 2.

The summary of different azimuthal quantum numbers for principal quantum number

The value of principal The value of azimuthal The number The symbol of sub-
quantum number (n) quantum number (l) = n-1 of sub-shells shells

1 (starting from zero) 1 s
2 2 s and p
3 0 3 s, p and d
4 4 s, p, d and f
0, 1

0, 1, 2

0, 1, 2, 3

The maximum number of electrons in each sub-shell can be calculated by using a formula
2(2l+1).

For example, in l = 2, the maximum number of electrons = 2 (2l+1) = 2 (2×2+1) =10. Here, l = 2
denotes d sub-shell which contains 10 electrons.

Magnetic quantum number (m) z z z
p, orbital y
The shape of the sub-shells (orbitals) Pr
is described by the azimuthal quantum Pyorbital
number. However, the same shape of the
sub-shell can have different orientations
in the space. For example, the orientation
of px, py and pz is shown in the diagram
alongside.

Optional Science - 10 139

CHEMISTRY

The same orbital having different orientation shows different effect in an atom. This effect
was first observed in presence of magnetic field. Therefore these numbers are called magnetic
quantum number. Magnetic quantum number is the third set of quantum number which
describes the orientation of the sub-shells. It is denoted by the letter "m". The magnetic
quantum numbers can have the values from –l to +l.

For example:

Azimuthal quantum Magnetic quantum Possible orientation
number (l) number (m)
0 Single orientation as it is "s" orbital
0 Three orientations (px, py and pz) as it is "p"
1 orbital
-1, 0 +1 Five orientations (dxy, dyz, dzx,dx2, dy2 and dz2)
2 as it is "d" orbital
-2, -1, 0, +1, +2

Memory Plus

In p sub-shell there are a total of three boxes denoted by px, py and pz. Each box can
contain two electrons having opposite spin. So, p sub-shell can contain total 6 electrons.

Filling of electrons takes place first single in all boxes and then starts for doubling. For
example, if there are five electrons in p sub-shell, then electrons fill like

Spin quantum number (s)

Electron not only revolves around the nucleus but also spins about its own axis. It can be
compared with the revolution and rotation of the earth around the sun and along the axis
respectively. Electrons spin in two ways. They are clockwise and anticlockwise. The clockwise
spin is called up spin ( ). It is given by the value s = +¹/₂. Similarly, the anticlockwise spin is
called a down spin ( ) and it is given by the value s = -¹/₂. Thus, the quantum number which
indicates clockwise and anticlockwise spin of an electron is called spin quantum number.

Example: 1

Write down the value of quantum number for the last electron in the electronic configuration
3s1.
Ans : For 3s1

1. Principal quantum number (n) = 3 (Because it is 3rd shell)
2. Azimuthal quantum number (l) = 0 (Because it is s-subshell)
3. Magnetic quantum number (m) = 0 (Because it is s-subshell which has single orientation)
4. Spin quantum number (s) = +¹/₂(Because it is up spin)

Example: 2

What are the quantum numbers for the last electron of the chlorine atom.
Ans : For 1s2 , 2s2 2p6, 3s2 3p5

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1. Principal quantum number (n) = 3 (Because it is 3rd shell)

2. Azimuthal quantum number (l) = 1 (Because it is p-sub shell)

3. Magnetic quantum number (m) = 0 (Because fifth electron lies in py)
4. Spin quantum number (s) = -1/2 (Because it is down spin)

Example: 3

What are the quantum numbers for the seventh electron of the sodium atom.
Ans : For 1s2 , 2s2 2p6, 3s1

The seventh electron lies within 2p. So,

1. Principal quantum number (n) = 2 (Because it is 2nd shell)

2. Azimuthal quantum number (l) = 1 (Because it is p-sub shell)

3. Magnetic quantum number (m) = -1 (Because seventh electron of sodium lies in pz)
4. Spin quantum number (s) = +1/2 (Because it is up spin)

Solution

When two or more chemically non-reacting substances are added to each other, they form
a mixture. Mixture may be heterogeneous or homogeneous. In heterogeneous mixture, the
mixing components can be seen easily but in homogeneous mixture, the mixing components
cannot be seen by our naked eyes. Solution is an example of homogeneous mixture. Thus, the
homogeneous mixture of solute and solvent is called solution. In solution, the composition
can be varied within a certain limit. The solution which contains water as a solvent is called
aqueous solution. Similarly, the solution which contains solvent other than water like benzene,
ether, petrol, kerosene, etc. is called non-aqueous solution.

Concentration of the Solution

The amount of solute dissolved in a given amount of solvent is called concentration.
Generally, the relative concentration is denoted by "dil" for dilute solution and "conc" for the
concentrated solution. Dilute and concentrated are the relative terms. They do not indicate the
exact concentration of the solution. Hence, different concentration units are used to express the
exact concentration of the solution. Percentage, gram per litre, normality, molarity, molality,
mole fraction, etc. are some units of concentration. Among them, some are explained below.

1. Percentage

Percentage is used to express the mass or volume of solute present in 100 g or 100 mL of
solution. The percentage composition is the expression of mass of solute in 100 parts of
volume of the solution. The percentage composition is written as:

i. Percentage by mass (% w/w)
Rohan scored 65 % in class IX final example. It means, he got 65 marks out of 100 full
marks. Similarly, percentage solution is also expressed in 100 g solution. Thus, the
amount of solute present in 100 g of solution is called percentage by mass.

Percentage by mass (% w/w) Mass of solute in gram
× 100

Mass of solution in gram

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For example: 30% sugar solution means, 30 g sugar is present in 100 g of the sugar
solution.

ii. Percentage by volume (% w/v)

When the amount of dissolved solute is measured in gram (g) and the amount of solution
is measured in 100 ml, it is called percentage by volume.

Percentage by volume (% w/v) = Mass of solute in gram × 100

Volume of solution in ml

For example: 25% glucose solution means, 25 g glucose is present in 100 ml of the glucose
solution.

iii. Percentage by volume (% v/v)

When the amount of dissolved solute is measured in ml and prepared solution is
measured in 100 ml, it is called percentage by volume.

Percentage by volume (% v/v) = Volume of solute in mL ×100

Volume of solution in mL

For example: 20% sulphuric acid solution means, 20 ml sulphuric acid is present in 100
ml of the solution.

2. Grams per litre

The gram mass of solute in one litre of solution is called grams per litre. In gram per litre,
the mass of solute is expressed in gram and the volume of solution is expressed in litre. It
is often used to describe the concentration of a solid in a solution. It is represented by g/l.

Mass of solute in gram
Gram per liter (g/ l) =

Volume of solution in litre

Gram per liter (g/ l) = Mass of solute in gram ×1000

Volume of solution in m l

For example: 25 g/l calcium chloride means, 25 grams of calcium chloride is present in
one litre of solution(1000 m l of solution).

3. Molarity (M)

Molarity (M) is the number of moles of solute present in one litre of solution. i.e.,
Number of moles of solute

Molarity =
Volume of solution in liter

Molarity = Number of moles of solute ×1000

Volume of solution in ml

We know that, the number of moles of any substance can be calculated dividing the
mass of solute by its molar mass.

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Example: 1

Calculate moles of methane in 64 g of methane.

Solution: Here, mass of methane = 64 g

Molar mass of methane = 16

Mass of methane 64
Moles of methane = = =4
Molar mass 14

Thus, the molarity of a substance can be calculated by using the following formula.

Molarity = Mass of solute × 1000

Molar mass Volume of solution in ml

Molar solution

Sometimes only one mole of a solute is present in 1000 ml of solution or one litre of solution.
It is called molar solution. Thus, the solution containing one mole of solute in one litre of
solution is called molar solution. For example, if one mole of hydrochloric acid (36.5 gram) is
present in one litre of solution, it is called molar solution of hydrochloric acid.

Decimolar solution

If a solution contains 1/10 mole of a solute in one litre solution, then it is called decimolar
solution. For example, if 1/10 mole of nitric acid (6.3 gram) is present in one litre of solution, it
is called decimolar solution of nitric acid.

Activity

To prepare 1 molar solution of sodium chloride (NaCl)
• Measure 58 g of NaCl crystals and keep into the one litre volumetric flask.
• Add some water and stir it to make a homogeneous solution.
• Fill water in the volumetric flask to make one litre.
• It is now one molar (1 M) salt solution.

4. Molality

In some solution, we measure solute in mole and solvent in kg. It is called molatity.
Therefore, molality (m) is defined as the number of moles of solute present in one
kilogram of solvent.

Number of moles of solute
Molality =

Mass of solvent in kilogram

Molality = Number of moles of solute ×1000

Mass of solvent in gram

The molality of the solution does not change with temperature. If 98 gram (1 mole) of
sulphuric acid is dissolved in 1000 gram of water, then it is called molal solution of
sulphuric acid.

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Molarity and Molality are completely different physical quantities. Molarity is measured
in mol/litre of solution while molality is measured in mol/kg of solvent.

Differences between molarity and molality

S.N. Molarity S.N. Molality

1. Molarity (M) is the number of moles of 1. Molality (m) is the number of moles of

solute present in one litre of solution. solute present in one kilogram of solvent.

2. Molarity is measured in mol/litre of 2. Molality is measured in mol/kg of solvent.

solution.

Memory Plus

For water as a solvent, molarity and molality have nearly same values. It is because 1 litre of
water nearly weighs 1 kg. But, for other solvents like CCl4, oil etc., the values are different.

Activity

To prepare 1 molal solution of sodium chloride (NaCl)
• Take 58 g of NaCl in a beaker. It is molar mass of sodium chloride.
• Keep exactly one kilogram of water in the beaker and stir to make solution.
• Now, it is 1 molal solution of NaCl in water.

Example: 1

Calculate the molarity of 40g H2SO4 in 200 ml solution.
Solution:

Given, mass of solute = 40g

Volume of solution = 200 ml

We know that molar mass of H2SO4 = 98 g

Again, number of moles of H2SO4 = Mass of solute solute = 40g = 40
Molecular weight of 98g 98

Also, volume of solution in litres = 200 = 1
1000 5

Now, Molarity (M) = moles of solue = 40/98 = 2.04 M
litres of solution ¹/₅

Example: 2

Calculate the molality if 90 g of NaCl is added into 1800 grams of water.
Solution:

Given, mass of solute = 90g
Mass of solvent = 1800 g
We know that molar mass of NaCl = 58 g (approx)

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Number of moles of NaCl = Mass of solute solute = 90g
Molecular weight of 58g

Mass of solvent in kg = 1800 = 9
Now, Molality (M) = 1000 5
Moles of solute 90/58
= ⁹/₅ = 0.86M
Mass of solvent in kg

5. Normality

The number of equivalents of a solute present in one litre of solution is called normality
(N). It means that normality is the number of mole equivalents in one litre of solution.

Number of equivalents of solute
Normality =

Volume of solution in litre

Number of equivanents of solute
Normality =

Volume of solution in mL

Normality = Mass of solute in gram × Volume 1000 in ml
Equivalent mass of solution

Normal solution (1 N)

The solution containing one equivalent of solute in one litre of solution is called normal
solution. For example, if 36.5 g of hydrochloric acid (one equivalent) is present in one litre
of solution, then it is called normal solution of HCl. Similarly, if 49 g of sulphuric acid (one
equivalent) is present in one litre of solution, then it is called normal solution of sulphuric acid.

Decinormal solution (N/10 )

The solution containing 1/10 equivalent of solute in one litre of solution is called decinormal
solution. For example, if 3.65 g of hydrochloric acid (N/10 equivalent) is present in one litre of
solution, then it is called decinormal solution of HCl. Similarly, if 4.9 g of sulphuric acid (N/10
equivalent) is present in one litre of solution, then it is called decinormal solution of sulphuric
acid.

Generally, we use normality for acids and bases. To calculate normality, we need to find out

the mole equivalent of the solution. The mole equivalent of an acid and a base can be calculated

by using the following formula.

Equivalent mass of acid = Molar mass of acid (Here, basicity means number of replaceable
hydrogens) Basicity

For example:

i. In HCl, there is one replaceable H+ ion. Therefore, basicity of HCl is 1.

ii. In H2SO4, there are 2 replaceable H+ ions. Therefore, the basicity of H2SO4 is 2.

Equivalent mass of base = Molar mass of base (Here, acidity means the number of
Acidity
replaceable hydroxyl ions)

For example:

i. In NaOH, there is one replaceable OH- ion. Therefore, acidity of NaOH is 1.

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ii. In Al(OH)3, there are 3 replaceable OH- ions. Therefore acidity of Al(OH)3 is 3.
Similarly, to calculate equivalent weight of salt, the total charge in cation or anion is used
in place of acidity and basicity. For example, MgCl2 = Mg2+ + 2Cl- , in MgCl2, the total
charge in magnesium ion is 2. Hence, it is used to calculate equivalent weight.

In the solution, if molarity is given, the normality can be calculated by multiplying with
acidity of a base or basicity of an acid.

Normality = n × Molarity (where n is acidity or basicity)

Memory Plus

The normality of a solution is equal to its molarity, if acidity or basicity is one.

For example:
a. For an acidic solution,

2 M of H2SO4 solution is the same as 4 N H2SO4 solution as its basicity is 2.
2 M of HNO3 solution is the same as 2 N HNO3 solution as its basicity is 1.
b. For a basic solution,
4 M Ca(OH)2 solution is the same as 8 N Ca(OH)2 solution as its acidity is 2.
4 M NaOH solution is the same as 4 N NaOH solution as its acidity is 1.

Example: 1

Calculate the normality of the following.
a. 4 M of H2SO4
b. 12.5 g of calcium carbonate in 200 ml of solution

Solution:
a. Given, Molarity of the solution (M) = 4

n factor of H2SO4 = 2
As we know, Normality (N) = n × M = 2 x 4 =8

b. Given, Mass of solute = 12.5 g

Molar mass of calcium carbonate = 100 g

"n" factor of calcium carbonate = 2

Solution = 200 ml

Equivalent mass of calcium carbonate = Molar mass = 100 = 50
"n" factor 2

Normality(N) = Mass of solute in gram × Volume 1000 in ml
Equivalent mass of solution

Normality (N) = 12.5 × 1000
50 200

Normality (N) = 1.25 N

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Answer writing skill I

1. What is Molecular mass? Illustrate with any two examples.

Ans: The sum of atomic mass of all atoms present in a molecule is called molecular mass.
For example, the molecular mass of methane (CH4) is 16 and molecular mass of calcium
carbonate (CaCO3) is 100.

2. What is Avogadro’s number?

Ans: Avogadro’s Number is the number of atoms, molecules, ions or particles present in one
mole of a pure substance. It is equal to 6.022 × 1023.

3. What are quantum numbers? Write down their names with symbol.

Ans: The characteristics of an electron and its position are determined by a set of specific
numbers called quantum number. There are four quantum numbers. They are:

i. Principal quantum number (n)
ii. Azimuthal quantum number(l)
iii. Magnetic quantum number (m)
iv. Spin quantum number (s)
4. Define normality (N). At which condition the normality and molarity is equal?

Ans: The number of equivalents of a solute present in one litre of solution is called normality (N).
If "n" factor of a solution is one, then normality and molarity become equal. For example,
one molar solution of HCl, NaOH, NaCl, etc. have molarity and normality equal.

5. Write down any two differences between atomic mass and molar mass.

S.N. Atomic mass S.N. Molar mass

1. The sum of mass of protons and 1. The total mass of atoms present in a

neutrons is called atomic mass. molecule is called molar mass.

2. It depends upon number of protons 2. It depends upon total number of

and neutrons present in the nucleus. atoms present in the molecule.

Example: potassium = 39 amu Example: sulphuric acid = 98 amu

6. The molecular mass of nitrogen molecule is 28 amu. What does it mean?

Ans: The molecular mass of nitrogen molecule is 28 amu. It means that, the sum of atomic
mass of nitrogen molecule is 28 or it is 28 times heavier than ¹/1₂th mass of carbon-12
isotope.

7. Write a short note about principal quantum number.

Ans: The principal quantum number represents the main energy level or shell to which the
electrons belong to. It decides the size of the shell and the average distance of the shell
from the nucleus. The principal quantum number is denoted by the symbol "n". It has
non-zero values like 1, 2, 3, 4 or K, L, M, N. The maximum number of electrons present
in each principal quantum number is calculated by using 2n2 formula.

CHEMISTRY 0Optional Science - 10 147

8. Calculate the molarity of 80 g H2SO4 in 400 ml solution.
Solution:

Given, mass of solute = 80g
Volume of solution = 400 ml
We know that molecular weight of H2SO4 = 98 g
Again, number of moles of H2SO4 = -MolecuMlaar-sswoefigsohltuote-f solute = 9-880gg = 8980

Also, volume of solution in litres = 400 = 2
1000 5

Now, Molarity (M) = moles of solue = 80/98 = 2.04 M
litres of solution ²/₅

9. Show the sub-shell electronic configuration of potassium and write down
the quantum number for the last electron.

Ans: The sub-shell electronic configuration of potassium (K) is 1s2 , 2s2 2p6, 3s2 3p6, 4s1

Here, the last electron lies in 4s1

So, principal quantum number (n)= 4 (As the last electron lies in 4th shell)

Azimuthal quantum number (l) = 0 (As it has 's"sub-shell)

Magnetic quantum number (m)= 0 (For the value of "l"= 0 the value of "m" = 0))

Spin quantum number (s)= +1/2 (As the electron is in up spin)

10. Write down all four quantum number for the eighth electron in the given
electronic configuration. (S) = 1s2 , 2s2 2p6, 3s2 3p4

Ans: Here, the eighth electron lies in 2p6

So, principal quantum number (n)= 2 (As the last electron lies in 2nd shell)

Azimuthal quantum number (l) = 1 (As it has 'p"sub-shell)

Magnetic quantum number (m)= -1 (because the 8th electron lies in px orbital)
Spin quantum number (s)= -1/2 (As the electron is in down spin)

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----Exercise J•Q- ---------

1Step

1. Define the following terms.

i. Atomic mass ii. amu

iii. Molecular mass iv. One mole

v. Molar mass vi. Avogadro’s Number

2. What is Quantum number? Write down their name.

3. Write very short about

i. Principal quantum number

ii. Azimuthal quantum number

iii. Magnetic quantum number

iv. Spin quantum number

4. Write down definition with formulae for the following:

i. Percentage by mass ii. Percentage by volume

iii. Grams per litre iv. Molarity

iv. Molality v. Normality (N)

5. What is molar solution.

6. Define decimolar solution.

7. What is molality (m)

8. Define normal solution.

9. Define decinormal solution.

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2Step

1. Write down any two characteristics of an atom.

2. How many molecules are there in one mole of water?

3. What information does principal quantum number give?

4. Write down the relation of atoms, ions, molecules with Avogrado’s number.

5. Give reason.
i. Inert gases are called monoatomic molecules. Why?
ii. The molecular mass of oxygen molecule is 32 amu. What does it mean?

6. Differentiate between:
i. Molarity and molality
ii. Atomic mass and molar mass
iii. Normal solution and molar solution

3Step

1. Calculate molecular mass of calcium carbonate (CaCO3) and ammonium carbonate
(NH4)2CO3

2. Calculate the molar mass of NaNO3 and find the number of molecules present in 2 mole
of NaNO3.

3. Calculate the number of molecules present in 1 kg of water and 1 kg of carbon dioxide.

4. Write down the value of quantum number for the last electron in the electronic configuration
2s1.

5. What are the quantum numbers for the last electron of the chlorine atom?

6. Calculate the molarity of 20 g of H2SO4 in 100 ml solution.
7. Calculate the molality if 45 g of NaCl is added into 900 g of water.

8. Calculate the normality in 2 M of H2SO4
9. Calculate normality if 0.0345 g of sodium carbonate is present in 300 ml of solution.

10. Calculate the number of molecules in 36 g water.

11. What is the molality of a solution prepared by dissolving 5 g of toluene(C7H8) in 225

grams of Benzene (C6H6)?

12. Calculate the molarity of 40 g H2SO4 in 100 ml solution.

13. Calculate the molality if 90 g of NaCl is added into 450 g of water.

14. Calculate the normality of a 4.0 molar sulphuric acid solution.

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