LOWER SECONDARY SCIENCE TEXTBOOK

Review Questions

1 Which of the following substances is necessary for photosynthesis?
A Soil
B Sugar
C Oxygen
D Carbon dioxide

2 Which of the following equations summarises the process of
photosynthesis?
A Carbon dioxide + Water Light energy Glucose + Oxygen

Chlorophyll

B Oxygen + Glucose Light energy Carbon dioxide + Water

Chlorophyll

C Carbon dioxide + Glucose Light energy Oxygen + Water

Chlorophyll

D Carbon dioxide + Oxygen Light energy Glucose + Water

Chlorophyll

3 Which of the following statements about fats is true?
A Fats keep us warm.
B Fats cannot be digested.
C Fats prevent constipation.
D Fats repair worn-out tissues.

4 Which diet, along with an unhealthy lifestyle, is likely to cause obesity?
A Eating a lot of fruits
B Eating a lot of yoghurt
C Eating a lot of vegetables
D Eating a lot of beef burgers

5 Which of the following does not contain food additives?
A Fruits
B A can of sardines
C Home-made cookies
D A carton of fresh milk

75Plant and Animal Nutrition

6 Why does food need to be digested?
A It is because food particles are too large to be absorbed.
B It is because food particles release energy during respiration.
C It is because food particles are too small to be stored in
the body.
D It is because food particles may contain bacteria which will
be killed by hydrochloric acid.

7 Which one of the following is true of enzymes?
A Enzymes are carbohydrates.
B Enzymes slow down chemical reactions.
C Enzymes are chemically changed at the end of the experiment.
D Enzymes help to break down large particles of food into
smaller particles.

8 What is the f inal product of protein digestion?
A Glycerol
B Fatty acids
C Amino acids
D Simple sugars

9 In which one of the following parts of the digestive system does
digestion of carbohydrates occur?
A Mouth and stomach
B Mouth and small intestine
C Stomach and large intestine
D Small intestine and large intestine

10 Which one of the following statements about the stomach is false?
A The stomach is a muscular organ.
B Digestion of proteins begins in the stomach.
C The stomach secretes carbohydrase together with protease.
D The hydrochloric acid in the stomach helps protease to work.

76 Plant and Animal Nutrition

11 Faridah wanted to f ind out the factors that would affect photosynthesis.
She prepared four set-ups using identical plants as shown below and
placed them near an open window.

Glass casing

Chemical Beaker
that Water
absorbs
carbon Glass casing
dioxide

Set-up A Set-up B

Beaker

Chemical
that
absorbs
carbon
dioxide

Set-up C Set-up D

In which one of her set-ups, A, B, C or D, would she expect the plant
to photosynthesise?

12 State the harmful effects of food additives in children.

13 In which parts of the human alimentary canal do the digestion of
fats occur?

14 Name a substance that is not digested before being absorbed by the
large intestine.

77Plant and Animal Nutrition

Chapter Electricity

13 During a thunderstorm, we often see huge lightning bolts darting
down from the sky. A bolt of lightning is a sudden surge of
electricity between the sky and the Earth. A single lightning bolt
has enough energy to light hundreds of light bulbs for a day or to
make a hundred thousand pieces of toast!

Firman Allah Subhanahu Wa Ta’ala
Tafsirnya:
Dan antara tanda-tanda kekuasaanNya
ialah Dia memperlihatkan kilat kepada
kamu untuk menakutkan (dengan
panahan petir) dan memberi harapan
(untuk turunnya hujan) dan Dia
menurunkan hujan dari langit lalu Dia
menghidupkan bumi sesudah matinya
dengan hujan itu. Sesungguhnya pada
yang demikian itu benar-benar terdapat
tanda-tanda (kekuasaan Allah) bagi
kaum yang (mahu) menggunakan akal
(untuk berfikir). (24)

And among His Signs is that He shows
you the lightning, for fear and for hope,
and He sends down water (rain) from the
sky, and therewith revives the Earth after
its death. Verily, in that are indeed signs
for people who understand. (24)

(Surah Ar-Rum: 24)

Let’s Explore

• What is electric current?
• What is voltage and resistance?
• How are electric circuits

represented?
• What are the differences between

series circuits and parallel circuits?
• What are the safety rules when

using electricity?

78 Electricity

13.1 Electric Circuits A
Ammeter
You should be able to:
• state that electric current is the flow of electrons;
• state that the dry cell drives the electrons around a closed

circuit in one direction;
• state ampere (A) and volt (V) as the S.I. units of current

and voltage respectively;
• identify symbols of simple electrical components (dry cell,

switch, bulb, resistor, ammeter and voltmeter);
• set up simple electrical circuits in series and parallel

arrangements;
• draw simple electrical circuit diagrams for series and parallel

circuits;
• investigate how to connect ammeters and voltmeters to an

electric circuit and take readings;
• calculate current and voltage in series and parallel circuits;
• investigate the effects of increasing the number of:

i) cells in series and parallel, and
ii) bulbs in series and parallel by measuring the voltage and

current flow.

What is electricity?

Electricity is a form of energy and is useful because it can
be easily converted to other types of energy. For example, at
home, electrical energy can be converted into light energy in
light bulbs, heat energy in a microwave oven as well as sound
energy in a sound system.
Where does our electricity come from?
In Brunei Darussalam, electricity is produced from natural gas,
which is used to power turbines and generators.

Current

To make an electrical appliance work, electrical charge must
flow through it. This movement of electrical charge is called
electric current (I).
An electric current is the flow of electrons. The path that the
current flows through is known as a circuit.
Current is measured with an ammeter. The S.I. unit of current
is ampere (A).

Electricity 79

When scientists f irst discovered current f low, they did not
know that this was due to the movement of particles called
electrons. They thought current f lowed from the positive
terminal to the negative terminal of a dry cell. This is known
as the conventional current flow.

Direction of conventional Direction of electron flow
current flow

When electrons were discovered, scientists realised that
electrons actually f low from the negative terminal to the
positive terminal of a dry cell. All circuit diagrams in this
chapter will show conventional current.

Voltage

When current f lows from one terminal of the dry cell to the
other, energy is needed to move the electric charge. The
amount of energy needed to push the charge can be referred
to as the voltage.
The voltage across an electrical component is measured with a
voltmeter. The S.I. unit of voltage is volt (V).

V

Voltmeter

80 Electricity

Circuits

When we connect various electrical components in a loop, they
form an electric circuit.

Dry cell
It is the source of
electrical energy.

Switch Light bulb
It is used to close It lights up when
or open the circuit. the current flows
Wires through it.
They connect the various
electrical components
and provide a complete
path for the current.

Components of a simple electric circuit

Open and closed circuits
When the switch is ‘off’, the circuit is open. Current cannot flow
through it because the path from one terminal to another is
not complete. The bulb will not light up.

Dry cell Switch
Bulb

An open circuit

When the switch is ‘on’, the circuit is closed. Current can flow
through it because the path from one terminal to another is
complete. The bulb will light up.

Switch

Dry cell

Bulb

A closed circuit

Electricity 81

Drawing circuit diagrams
The following table summarises the circuit symbols commonly
used.

Component Circuit symbol
A dry cell

Science Smart A switch (open)
A light bulb (closed)
Learn how to use the
symbols in this table
to draw your circuit
diagrams.

A resistor
A variable resistor or rheostat

An ammeter

A voltmeter A
V

WB Link Activity 13.1
82 Electricity

The simple electric circuit shown on page 81 can be
represented with a circuit diagram as shown below.

A circuit diagram allows
us to represent an
electric circuit.

Series and parallel circuits
To light up a few bulbs at the same time, you can connect
them in two ways — in series and in parallel.
In a series circuit, there is only one path for the current to
flow through.

Dry cells

Bulbs

A series circuit Circuit diagram of a series
circuit

If one of the bulbs is taken out or damaged, the other bulb will
not light up. This is because the circuit is open, so no current
can pass through the circuit.

An open circuit

Electricity 83

In a parallel circuit, there is more than one path for the
current to flow through. Some current passes through one
bulb and the rest flows through the other bulb.

A parallel circuit Circuit diagram of
a parallel circuit

In a parallel circuit, if one of the bulbs is taken out or damaged,
the other bulb will still light up. This is because a part of the
circuit is still closed. This is why light bulbs in houses and other
buildings are usually connected in parallel.

An open circuit

Try this

How would you draw circuit diagrams for these circuits?
1) 2)

01

A

84 Electricity

Measuring current

An ammeter is used to measure current. To correctly measure
the current in a circuit, the ammeter must be connected in
series in the circuit. The ammeter’s terminals are marked
with positive (+) and negative (–) signs. The ‘+’ terminal
is connected to the ‘+’ terminal of the dry cell, and the ‘–’
terminal is connected to the ‘–’ terminal of the dry cell through
the bulb.

01 A WB Link Activity 13.2

A Circuit diagram with an
ammeter in a circuit
How to connect an ammeter
correctly

Measuring voltage

A voltmeter is used to measure voltage. To correctly measure
voltage across a particular component, the voltmeter must
be connected in parallel to the component. Again, the two
terminals have ‘+’ and ‘–’ signs. To measure the voltage across
a component, the ‘+’ terminal is joined to the ‘+’ terminal
of the dry cell, and the ‘–’ terminal is connected to the ‘–’
terminal of the dry cell.

01

V

V

How to connect a Circuit diagram with WB Link Activity 13.3
voltmeter correctly a voltmeter in a
circuit

Electricity 85

Calculating current in series circuits

In a series circuit, the current at every point of the circuit is
the same. As the number of bulbs increases, the brightness of
the bulbs decreases. If one bulb goes off or is removed, the
circuit is broken and no current f lows.

IA
1
AI
3
I
2
A
I1 = I2 = I3

Example 1
The diagram shows a circuit with an ammeter connected in
series.

I
1
I
3

I
2

A

If the ammeter reads 2.5 A, what is the value of I1 , I2 and I3?
Answer
Since the circuit is series,
I1 = I2 = I3 = 2.5 A.

86 Electricity

Calculating current in parallel circuits

In a parallel circuit, the current splits into two or more branches
in the circuit. If the bulbs are identical, as the number of bulbs
increases, the brightness of the two bulbs will be the same.
The total current of the circuit is the sum of the current that
passes through each of the branches. If one bulb is removed,
any remaining bulbs in parallel will still light up.

IT

I1
I2

IT = I1 + I2
Example 2
The diagram shows a circuit with an ammeter connected in
series to the dry cell. The bulbs are not identical.

I =6A A I =2A
T 1

I
2

If the ammeter reads 6 A, what is the value of I ?
2

Answer
I = I + I
6T A = 21 A +2 I
I = 6 A – 22 A
2 = 4 A

Electricity 87

Calculating voltage in series circuits

As mentioned before, in a series circuit, the current does not
split into two or more branches. However, the total voltage is
split between the components in the circuit. The total voltage
is equal to the sum of the voltages across each component in
the circuit.

Bulb 1 Bulb 2 Bulb 1 Bulb 2

VV V
12 T

VV V

Total Voltage (V3) = voltage across bulb 1(V1) + voltage across bulb 2 (V2)
VT = V1 + V2

Example 3
The following diagram shows a circuit with two bulbs in series
with a voltmeter connected across each of them.

V =6V
T
V

V V =2V
1 2
V
V

Find V .
1

V = V + V
6 TV = V1 + 22 V
So, V = 6 V – 2 V

= 4 V

88 Electricity

Calculating voltage in parallel circuits

As mentioned before, in a parallel circuit, current splits up into
two or more parts. However, the voltage across any component
is the same as the total voltage in the circuit.

V
1

V

V
2

V

V
3

V

V1 = V2 = V3
Example 4
The following diagram shows a circuit with two voltmeters
connected. One is parallel with the cell, and one is parallel
with a bulb.

V
1

V

V =8V
2

V

V
3

V

Find V1 and V3.
V = V = 8 V

12

Electricity 89

Cells in series

In a simple circuit, as the number of dry cells in series increases,
the voltage increases. The total voltage across all the dry cells
is equal to the sum of the voltages of the individual cells.

V

V

With one dry cell in a circuit, the voltage is 1.5 V.
V

V

With three dry cells in a circuit, the total voltage is 4.5 V.
V

V

When the two dry cells face each other, their voltages cancel each other out.
Hence, for the above circuit, the voltage across the three dry cells is 1.5 V
(the voltage of the remaining dry cell.)

90 Electricity

Cells in parallel

As the number of identical dry cells in parallel increases, the
total voltage across the dry cells remains the same as the
voltage of each dry cell.

V

V

With one dry cell, the voltage is 1.5 V.

Connecting two dry cells in parallel is like replacing smaller dry
cells with a larger one of the same voltage. If one dry cell can
be used for fours hours, then two dry cells in parallel will last
eight hours.

V

V

With two dry cells in parallel, the voltage is still is 1.5 V.

Electricity 91

Relationship between voltage and current
As the number of dry cells in series increases, the total voltage
increases. Does the current also increase? The following
diagrams explain what happens.

One dry cell produces an electric current. Two dry cells in series give a higher voltage.
The bulb lights up. The current is greater and the bulb is brighter.

As the voltage in a circuit increases, the current also increases.

The table below summarises the effects on the brightness of
bulbs and voltage in the circuit when identical dry cells are
added and connected in series and parallel.

More dry cells Series Parallel
(Number of bulbs • Brightness of • Brightness of bulbs
unchanged) bulbs increases stays the same
• Voltage increases • Voltage across the
across the cells cells stays the same

Bulbs in series

If two identical bulbs are connected in series, the current
passing through each bulb is the same. Each bulb will have
the same brightness.

A

A

V V

Circuit 1 with two bulbs in series

92 Electricity

Bulbs in parallel

If an identical bulb is added to the circuit in parallel, the current
splits into two branches. Each branch carries a current of 3 A,
therefore each bulb has a current of 3 A passing through it. As
a result, each bulb has the same brightness.

A I =3A
A I =6A 1

T I =3A
2

Circuit 2 with two bulbs in parallel

I = I + I
T = 31 A + 23 A
= 6 A
The table below summarises the effects on the brightness
of bulbs and voltage in the circuit when identical bulbs are
connected in series and parallel.

Series Parallel

More bulbs • Brightness of bulbs • Brightness of bulbs
(Number of decreases stays the same
dry cells
unchanged) • Voltage across each • Voltage across each
bulb is the same bulb is the same

Quick Check Activity 13.4,

1. What is the purpose of a switch? WB Link 13.5 & 13.6
2. Describe the difference between an open circuit and a

closed circuit.
3. Do households use parallel or series circuits?
4. What is used to measure the voltage between two

points in an electrical circuit?
5. State the S.I. unit used for;

a) electric current, and
b) voltage.

Electricity 93

13.2 Resistance

You should be able to:
• infer that a resistor will reduce the current in an electric

circuit;
• state the S.I. unit of resistance as ohm (Ω);
• calculate the effective resistance when resistors are

connected in series and parallel.

All electrical components have a property known as
resistance, which opposes the current in a circuit. The S.I.
unit of resistance is ohm (Ω).
Resistors are electrical components that can be used to
control the size of the current in a circuit.

Types of resistor

There are two types of resistors – fixed resistor and variable
resistor. A fixed resistor has a resistance that does not
change. The symbol for a fixed resistor is:

Science Bites Symbol for a fixed resistor

Did you realise that To vary the current in the circuit, we use a variable resistor
a bulb also acts a (also known as rheostat). The symbol for a variable
resistor? You can resistor is:
achieve the same
effect in Circuit 2 Symbol for a variable resistor
if an extra bulb
is added in series If a resistor is added to a circuit, the current is reduced. Adding
instead of a resistor. a resistor in series, makes the bulbs in Circuit 2 dimmer than
the bulbs in Circuit 1.

Switch

Dry cell

Bulb Resistor

Circuit 1 Circuit 2

94 Electricity

Resistors in series and parallel

The resistance of a circuit can be varied by connecting resistors
in different ways. Resistors can be connected in series or in
parallel.

Resistors in series
Look at the circuit diagrams below. The f irst diagram has two
trhesroisutgohrs b, oRt1h a rneds iRs2t,o arrsr.a Inng tehde i nse sceornieds .d Tiahger asmam, Re c aunrrde nRt fh loawves
been replaced by a single resistor, R . 12

T

R R x amperes x amperes
12 R
≡
T
equivalent to

The total resistance in both the circuits is the same. The same
current f lows in each circuit.

The example above shows that the total resistance in the
circuit (R ) is equal to the sum of the separate resistances.
This can bTe represented as:

R R R
T 12
∫

Or,
Total resistance (R ) = Resistance (R ) + Resistance (R )
T = R + R 1 2

R T12

Example
Look at the circuit diagram below. What is the total resistance?

≡

R = 6 Ω R = 2 Ω R
12 T

R = R + R Equivalent circuit
R T = 6 1Ω + 22 Ω

T = 8 Ω

Electricity 95

Resistors in parallel
Look at the circuit diagrams below. The f irst diagram shows
two resistors in parallel.

x amperes x amperes
R
≡
T
R
1

R
2
Equivalent circuit

The total resistance in both circuits is the same. The total
current in each circuit is the same. Therefore, the two circuits
are equivalent.

We can f ind that the total resistance from the following formula:
1 = 1 + 1
RT R1 R2

Example
Look at the circuit diagrams below. What is the total
resistance?

I I

R = 3Ω ≡ R = 2Ω
1 T

R = 6Ω Equivalent circuit
2

1 = 1 + 1
RT R1 R2

Quick Check 1 = 1 + 1 3
RT = + 6
1. What is the 3 1
function of a 2 = = 1
resistor?
6662
2. What is the
S.I. unit for ∴ R = 2 Ω
resistance?
T
96 Electricity
The example above shows that the total resistance is less than
either of the two separate resistances (R and R ).

12

13.3 Household Wiring
and Safety Devices

You should be able to:
• set up a circuit with two or more bulbs and switches to

operate them independently;
• explain the function of a fuse;
• identify the correct fuse rating for an electrical device with a

given current value;
• carry out wiring of a three-pin fused plug correctly;
• explain the function of earthing the metal casing of an

electrical appliance;
• describe safety rules in the use of electricity.

Switches

Switches are used to open or close circuits. In section 13.1,
you used simple switches. Another kind of switch is used to
select one out of two circuits. It is called the two-way switch.

Position 1

Position 2

Symbol for two-way Two-way switch in
switch a circuit

When the switch is at position 1, the top bulb lights up. When
the switch is at position 2, the bottom bulb lights up.

Electricity at home
In the home, electrical lighting and appliances are connected in
parallel. If one lamp or appliance is faulty or is not connected,
the other lamps will still work.

Power supply Two-way
Two-way switch
switch

The two-way switch helps Ahmad to switch on and off the light as he moves
from the door on the left to the one on the right.

Electricity 97

Switches in parallel circuits

In parallel circuits, switches can be used to control bulbs
separately.

Switch ‘off’ Switch ‘on’

≡ Bulb A
Bulb B

The circuit diagram above has one switch. When the switch
is switched off, the bulbs do not light up. When the switch is
switched on, both bulbs light up. Look at the diagrams below.

? Bulb A Bulb A lights
up but Bulb
Is the lighting in your A ‘on’ Bulb B B does not.
classroom a parallel Both bulbs
or series circuit? How B ‘off’ lights up.
do you know? Give
a reason for your A ‘off’
answer. B ‘off’

Bulb A

A ‘on’ Bulb B

B ‘on’

The circuit diagram above has two switches. When switch A is
switched on and switch B is switched off, only one bulb lights
up. When both switches are switched on, both bulbs light up.

Ahmad, is the It’ll definitely be the parallel
series or parallel circuit. In a parallel circuit,
circuit more
commonly used in if one bulb is damaged or
our homes? switched off, the other

bulb can still work. This is
an important advantage of a
parallel circuit.

98 Electricity

Fuse

Electrical components and appliances will work when a certain
amount of current passes through. If too much current f lows,
the component or appliance can be damaged or catch f ire. To
prevent this, a fuse is placed in the circuit.

A fuse and its circuit symbol

A fuse is a short length of wire of a certain diameter. It is made
of an alloy of tin and lead. It has a low melting point.
Fuses can be found in several places. Below are some examples
of fuses.

An electric plug with a fuse A fuse box in a building

A fuse is connected in series in a circuit as shown below.

A

A fuse in a circuit

Electricity 99

If too much current flows, the fuse becomes hot and melts. This
breaks the circuit and the current stops flowing. Therefore, the
fuse protects the component or appliance from being damaged
by the large current.

Increase
the
current

Bulb filament
melts and
breaks.
The bulb is
damaged.

Circuit without a fuse

Increase Fuse wire
the melts and
current breaks. The
circuit is
broken and
electricity
stops
flowing.
The bulb
does not
light up
but is not
damaged.

Circuit with a fuse

The rating of a fuse is the maximum current that can flow
through it without melting. Common fuse ratings are 0.1 A,
1 A, 3 A, 5 A, 13 A, 15 A and 30 A. A fuse with a rating of 1 A
melts if the current through it is greater than 1 A.

Fuses of different ratings

100 Electricity

Choosing the right fuse
The fuse rating that we choose should be slightly higher than
the maximum current in the circuit.

When the current in a circuit If a 1 A fuse is used in a 5 A
is 4 A, a fuse with a rating circuit, the fuse wire will melt.
that is slightly higher than
4 A should be used. My wire
has melted!
I am the
right choice!

If a 13 A fuse is used
instead, the excess current
will not be cut off. The
circuit may overheat and
catch fire!

I can’t stop this high
current from passing
through – I think the circuit
is going to catch fire!

Using the correct fuse

A toaster uses a current 3 A. Looking at the fuse ratings given
above, we should choose a fuse of 5 A.
A 13 A fuse cannot be used because it will allow a current that
is too large to pass through the toaster. This larger current will
damage the toaster.
We cannot use a fuse rating below 5 A because the toaster
requires a current of 3 A to work. A fuse with a rating below
5 A will melt very quickly and break the circuit.

Electricity 101

Correct way to wire a three-pin plug
The diagram below shows what a three-pin plug looks like with
its back opened. The electrical cable contains three colour-
coded wires.

Earth wire Live wire
Neutral wire Fuse

Three-pin plug with open back

The live wire (brown) carries
the current from the power
supply to the appliance.

The earth wire (green and
yellow) is connected from
the conducting part of the
appliance to the ground.

The neutral wire (blue)
carries the current from
the appliance back to the
power supply.
The cable contains three colour-coded wires.

Each wire is colour-coded. The table below shows the old and
new colour codes.

Wire Old Colour New Colour
Live Red Brown
Neutral Black Blue
Earth
Green Green and yellow

New and old colour codes of the wires

WB Link Activity 13.7 You will learn how to correctly wire a three-pin fused plug in
your workbook.

102 Electricity

Safety by earthing

What may happen if a metal kettle is not earthed? When a
loose bare wire from the live wire touches the metal kettle,
the metal kettle is said to be live. When a person touches the
kettle, he will get an electric shock. This is because the kettle
does not have an earth wire.

Live wire Live wire
touches the touches the
kettle kettle

L L
N N
E
Current flowing
through the body Current flow to
the ground

Without earth wire With earth wire

When an earth wire is connected to the metal kettle, most Rubber shoes
of the current will now flow through the earth wire to the protect workers
ground. This is because the earth wire has a lower resistance from electric shocks.
than the body.
People who regularly work with high voltage electrical
equipment are required to wear thick rubber shoes. The
resistance of the shoes is so high it would not let current flow
to the ground, through the person. Thus, they are protected
from electric shock.
Usually, appliances with metal surfaces are earthed, such
as washing machines, electric kettles, toasters and ovens.
Electrical appliances, which do not have exposed metal surfaces
such as hairdryers with plastic casings and light bulbs, are not
earthed.

Electricity 103

Overloading

If there are too many appliances connected in parallel to a
socket, the current in the mains wire increases, causing it to
get hot. The circuit is said to be overloaded and this may
cause a f ire.

Overloading

Electrical safety rules

We should observe electrical safety precautions to prevent
electric shocks and f ires.
1. Do not overload the same power socket with too many

plugs. This will draw a large current and generate heat in
the wires carrying the current to the socket, which may
cause a f ire.

Never overload a power socket.

104 Electricity

2. Do not insert objects other than electrical plugs into
power sockets as you may get an electric shock.

Never attempt this.

3. Do not touch electrical appliances with wet hands.

It is raining heavily Wait, Abdul! You’re all wet. … an electric shock
outside! You might get….

Never touch sockets with wet hands.

Electricity 105

4. If the electrical wiring is very old, and the insulation is
peeling off, this may cause electric shocks and f ires.

Replace old damaged wires.

5. Do not place electrical appliances near wet areas such as
the bathroom and sink.

Never use electrical appliances in wet places.

Science Bites

Water is a conductor of electricity. When it falls on an
appliance, it often acts as a connector from the live to the
neutral wires. Current then f lows through the water because
it has low resistance and not through the appliance. This
creates a short circuit.

106 Electricity

6. Disconnect the appliance from the power supply before Try this
doing repairs and maintenance.
Are our homes
Never clean an appliance safe? Conduct an
while it is switched on. investigation and look
for these hazards:
7. It is always safer to call the electrician to repair damaged • Are the electrical
electrical equipment.
sockets
overloaded?
• Are appliances
used near water?
• Are the power
cords worn or
frayed?
• Are appliances
close to flammable
liquids or other
dangerous
materials?
• Are heaters or
light bulbs close
to anything
flammable?

Call the electrician

Electricity is beneficial to us but without following the safety
rules, it can be hazardous. Remember to always follow the
safety rules when handling electrical equipment.

Quick Check

1. What is the function of a fuse?
2. Why must a fuse with the correct current rating

be used?
3. Name three household appliances that would need to

be earthed.
4. List three precautions we should take when using

electrical appliances.

Electricity 107

Summary

Electricity Open circuit Series circuit
Closed circuit Parallel circuit
Electric circuits
Electric S.I unit is ampere (A)

current (I) Series circuit: I = I = I = …
T12
Voltage (V)
Parallel circuit: I = I + I + …
Resistance (R) 12

Safety S.I unit is volt (V)
precautions Series circuit: V = V + V + …

108 Electricity T12

Parallel circuit: V = V = V = …
12

S.I. unit is Ohm (Ω)

Series circuit: R = R + R + …
T1 2

Parallel circuit: 1 = 1 + 1 …
RT R1 R2

Resistors

Fuses Fixed
Earthing Variable

Safety
rules

Review Questions

1 What do the symbols below represent?



A A bulb and a dry cell
B A dry cell and a switch
C A dry cell and a resistor
D A voltmeter and a resistor

2 Which one of these circuits has the highest total resistance?

A B

5 Ω 2 Ω 1 Ω
6 Ω 5 Ω

C D 4 Ω

1 Ω 3 Ω
5 Ω 3 Ω

3 Why are parallel circuits preferred to series circuits in households?

4 Write down the reading shown in each of the ammeters below.

a) b)

Electricity 109

5 Write down the reading shown in each of the voltmeters below.

a) b)

6 Draw the circuit diagram for the following circuit.

Ammeter

Cells

Bulb

Switch

7 Study the circuit diagram shown below and answer the questions.

X

S Y
1
SZ
2

Which bulb(s) light up when:
a) both switches S and S are closed?
b) switch S is clos1ed, but2 switch S is opened?
c) switch S1 is closed, but switch S2 is opened?

21

110 Electricity

8 What are the hazards of;
a) damaged insulation,
b) overloaded circuits, and
c) damp conditions when using electricity?

9 Examine the following circuit diagram. What will happen to the
brightness of the bulb and the reading of the ammeter when the
following changes are made?

VA
R

a) The resistance of rheostat R is increased. Give a reason.
b) Another dry cell is connected in series to the f irst dry cell. Give a

reason for your answer.
10 A hair dryer uses a current of 5 A. State what happens if a fuse of the

following ratings are used:
a) 3 A fuse, and
b) 13 A fuse?

Electricity 111

Chapter Acids and Alkalis

14 Acids and alkalis are everywhere around us. A puddle of rainwater
is slightly acidic. Many of our foods like oranges, lemons and
vinegar contain acids whereas cakes are made using alkalis.
A bee sting is acidic but a wasp sting contains an alkali. This
chapter will tell you more about acids and alkalis.

Firman Allah Subhanahu Wa Ta`ala
Tafsirnya:
Allah menciptakan setiap haiwan yang
bergerak itu daripada air, sebahagian
daripada haiwan itu ada yang menjalar
di atas perutnya dan sebahagiannya
berjalan dengan dua kaki dan sebahagian
lagi berjalan dengan empat kaki. Allah
menciptakan apa sahaja yang Dia
kehendaki kerana sesungguhnya Allah
Maha Berkuasa atas tiap sesuatu. (45)
Allah has created every moving (living)
creature from water. Of them, there are
some that creep on their bellies, and
some that walk on two legs, and some
that walk on four. Allah creates what He
wills. Verily, Allah is able to do all things.
(45)
(Surah An-Nur, ayat 45)

Let’s Explore

• What are the properties of acids and
alkalis?

• What are the effects of acidic,
alkaline and neutral solutions on
indicators?

• What happens when acids and
alkalis are mixed?

112 Acids and Alkalis

14.1 Properties of
Acids and Alkalis

You should be able to:
• list some common laboratory acids and alkalis;
• investigate the properties of acids and alkalis in terms of:
pH value, effect on litmus paper, corrosive nature, and

taste;
• investigate the effects of various solutions on litmus paper

and classify them as acids, alkalis or neutral solutions;
• investigate the degree of acidity or alkalinity of given

solutions using pH paper or Universal Indicator solution.

Acids Science Bites

In your school laboratory, there are a number of acids Acids are very
including hydrochloric acid, ethanoic acid, sulfuric acid and reactive. They react
nitric acid. These are colourless liquids but there are some with:
acids that are solids. • metals to produce
Some acids, such as citric acid, are natural and found in
citrus fruits like oranges and lemons. Others are made hydrogen gas, and
industrially and used to produce things we use daily. • carbonates to
Here are examples of common acids and their uses.
produce carbon
Acid Ethanoic acid Sulfuric acid dioxide gas.
Use (vinegar)
Nitric acid

It is used for cooking It is used in car It is used to make fertilisers.
and preserving food. batteries.
Common acids and their uses

Acids and Alkalis 113

Properties of acids
The following are the properties of acids.

Acids are corrosive
Acids can damage your clothes and burn your skin. When
handling acids, take extra care to ensure your safety by:
• wearing safety goggles to protect your eyes from acid
splashes, and
• wearing a laboratory coat.

If an acid accidentally
spills onto your skin,
wash the affected
area under running
water and inform your
teacher immediately.

Hazard symbol for corrosive substances

Acids taste sour
The sour taste in citrus fruits, e.g. oranges, lemons and
pomelos, is due to the citric acid in them.

The sour taste in oranges is caused by citric acid.

Acids turn blue litmus paper red
When red and blue litmus papers are dipped into an acidic
solution, the blue litmus paper turns red. The red litmus
paper remains unchanged.

Litmus test for acids

114 Acids and Alkalis

Alkalis

Alkalis are another group of chemicals found in everyday
life. Alkalis belong to a larger class of chemicals known as
bases. Alkalis are bases that are soluble in water. Sodium
hydroxide and potassium hydroxide are alkalis commonly
found in the laboratory. Both dissolve in water to form
alkaline solutions.

Here are examples of common alkalis and their uses.

Alkali Use
Ammonia

It is used to make fertilisers.
Sodium hydroxide

It is used to make soaps.

Potassium
hydroxide

It is used in alkaline batteries.
Common alkalis and their uses

Acids and Alkalis 115

Properties of alkalis
The following are the properties of alkalis.
Alkalis are corrosive
Alkalis are corrosive, they can cause severe damage to the
skin, eyes and respiratory tract.

Most hair dyes contain ammonia. Ammonia is a
corrosive alkali.

Alkalis taste bitter
If you have accidentally tasted soap or soap bubbles, you
will know that the soap solution tastes bitter. This is due to
the presence of alkalis in soap.
Alkalis turn red litmus paper blue
When red and blue litmus papers are dipped into an alkaline
solution, the red litmus paper turns blue. The blue litmus
paper remains unchanged.

Litmus test for alkalis

116 Acids and Alkalis

Alkalis have a soapy feel ?
The slippery feel of liquid detergents or soaps comes from
the alkalis in them. This is one of the more obvious feature Tasting and feeling an
of alkalis that distinguishes them from acids. unknown solution in
your school laboratory
is not a good way to
differentiate between
acids and alkalis. Why?

Soap contains alkali. WB Link Activity 14.1

Indicators

An indicator is a substance that changes colour depending
on whether the solution tested is acidic or alkaline.
Indicators can exist as solutions or in the form of indicator
papers. Some common indicators are red and blue litmus
papers, pH paper and Universal Indicator.
Litmus paper
The litmus paper test is a common way of f inding out if a
solution is acidic or alkaline. It however, does not give any
indication of how acidic or alkaline the solution is.

Using litmus paper to test if a solution is an acid
or alkali

1. Place a strip of red litmus paper and a strip of blue
litmus paper on a clean white tile.

2. Put two drops of the sample liquid onto each strip of
paper and observe any changes in colour.

3. The colour change on the litmus paper will indicate
whether the sample is acidic or alkaline.

Acids and Alkalis 117

Science Bites The pH scale
Sometimes, we may want to know how acidic or alkaline a
‘pH’ stands for solution is. To do this, we can use a pH scale.
‘potential of The pH scale is a range of values from 0 to 14. A pH of 0
hydrogen’, from the indicates that the solution has very high acidity. A pH of
French term pouvoir 14 indicates that the solution has very high alkalinity. A
hydrogène. neutral solution has a pH of 7.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neutral
Highly acidic Highly alkaline

Acidity increases Alkalinity increases

The pH scale

pH 0 – 1 pH 3 pH 7 pH 9 – 10 pH 13 – 14
Acid in car Orange Pure Soap Household
batteries water
juice cleaners

pH values of common household items

To determine the pH values of solutions, we use pH paper.
When dipped into a solution, the pH paper changes colour
depending on the pH value of the solution.

118 Acids and Alkalis

Universal Indicator
The pH value of a solution can also be determined using
Universal Indicator.
The Universal Indicator gives different colours when it is
added to solutions of different pH values.

Highly Neutral Highly
acidic alkaline

Colours of Universal Indicator in solutions of different pH values

The colours of pH paper and Universal Indicator in solutions
of different pH values can be summarised in the table below.

pH ranges Description Colour

0 – 3 Strong acid Red

4 – 6 Weak acid Orange/Yellow

7 Neutral Green

8 – 11 Weak alkali Blue

12 – 14 Strong alkali Purple

Colours of pH paper and Universal Indicator in solutions of
different pH values

Acids and Alkalis 119

Using pH paper and Universal Indicator to test the
pH of solutions

1. By dipping a piece of pH paper into a sample
solution, we can determine the pH value of the
sample solution by comparing the colour of the pH
paper with a reference colour chart.

2. We can repeat the experiment using Universal
Indicator solution instead of pH paper.

Activity 14.2 The colour of the pH paper is compared
with a reference chart to determine the
WB Link Activity 14.3 pH of a solution.

? Quick Check

In what situation 1. Name three common acids found in your school
would it be convenient laboratory.
to use litmus paper?
2. Describe one way of testing for the presence of acids.
When would it be 3. Name three common alkalis found in your school
more appropriate
to use Universal laboratory.
Indicator or pH paper? 4. Describe one way of testing for the presence of alkalis.

120 Acids and Alkalis

14.2 Neutralisation

You should be able to:
• define neutralisation as a chemical reaction where an acid

and an alkali react to form a salt and water;
• state the word equation for neutralisation;
• explain the importance of neutralisation in daily life.

Neutralisation

Neutralisation is a chemical reaction where an acid is
mixed with an alkali to form a salt and water.

The general word equation to represent the reaction of an
acid with an alkali is:

Acid + Alkali  Salt + Water Try This

For example, mixing hydrochloric acid with sodium Make your own
hydroxide produces two new substances: sodium chloride volcano using acid
and water. and alkali!
1. First, put a
hydrochloric + sodium  sodium + water
acid hydroxide chloride tablespoon of
baking powder in
Science Bites a plastic bottle
and place the
Pollutants released by automobiles and industries are bottle on a plate.
the main cause of acid rain. You might also
want to add food
To counter the effects of acid rain, lime (calcium colouring into the
hydroxide), is added to the affected water and soil to bottle.
neutralise the acids. 2. Then, use some
clay to cover the
sides of the bottle;
giving it the shape
of a volcano.
3. Finally, add some
vinegar, step back
and watch your
volcano erupt!
What you see is
caused by the
reaction of the
baking powder
(alkali) and the
vinegar (acid).
Carbon dioxide is
given off, causing the
mixture to flow out
of the bottle.

Acids and Alkalis 121

Neutralisation in daily life
There are many everyday uses of neutralisation.
Shampoos usually contain a mild alkali.
This causes hair strands to entangle
easily. Hair conditioners contain a mild
acid that neutralises the alkali, making
hair feel smoother and easier to manage.

After eating, food particles can Most facial cleansers are alkaline
remain on and in between the and may cause skin dryness.
teeth. When the food decays, Toners are usually acidic and are
it produces an acid that causes used to neutralise the alkalinity
tooth decay. Brushing with and restore skin to its normal pH.
toothpaste, which is alkaline,
neutralises the acid.

Neutralisation in everyday products

122 Acids and Alkalis

Effects of neutralisation on indicators
We have seen that mixing an acid with an alkali results in
the formation of a salt and water. What would we observe
when an alkali is slowly added to an acid containing an
indicator, such as Universal Indicator?
The colour changes that take place reflect the change in pH
values when an alkali is slowly added to an acid.

pH 1 pH 4 pH 7 pH 11 pH 14

The Universal Indicator goes through a range of colours as the
pH increases from 1 to 14.

Try This

Indicators can come from natural sources such as the red
cabbage. The juice of the red cabbage is usually purple,
but turns pink in acidic conditions and green in alkaline
conditions.
You can make your own indicator paper. Cut up some red
cabbage and put it in a pot. Cover it with just enough water.
Once it comes to a boil, switch off the stove and let the
liquid cool. Next, cut up some porous, white paper into
5 cm × 5 cm cards. Soak each card into the cooled liquid
and let it dry.
Pour a little vinegar onto your indicator paper and observe
the colour change. Is vinegar acidic or alkaline? Mix a little
baking soda with water and immerse your indicator paper
into it. What can you see? Is baking soda acidic or alkaline?

Quick Check Activity 14.4

1. Write a word equation for neutralisation. WB Link Activity 14.5
2. Name two uses of neutralisation in our daily lives.
3. Explain how the red cabbage can be used as a

natural indicator.

Acids and Alkalis 123

Summary

Acids and Alkalis

Acids Alkalis
have the following have the following
properties properties

• Corrosive • Corrosive
• Sour taste • Bitter taste
• Turn blue litmus • Turn red litmus

paper red paper blue
• pH < 7 • pH > 7
• Have a soapy

feel

react together to give
a salt and water
Neutralisation

Acid + Alkali  Salt + Water

124 Acids and Alkalis