ELECTRICITY AND MAGNETISM FORM 2 KSSM

CHAPTER: 7
ELECTRICITY AND MAGNETISM

7.1: ELECTRICITY

EnErgy

1. Energy means the ability to do work.

2. Energy is needed for:

a) Living things to carry out life processes like respiration, move and grow.
b) Non-living things to function and move for example robots and machines.

3. Energy cannot be created nor destroyed but can be
changed from one form to another.

4. Sources of energy:

a) Sun d) Water g) Radioactive substances
b) Wind e) Wave i) Fossil fuel
c) Geothermal f) Biomass

5. Types of energy:
Heat energy

Produced by burning or from hot objects

Electric
energy

Produced from the flow of electric charges

Kinetic energy

Produced by the moving objectEs nergy stored in the
nucleus atom
Elastic potential

energy

ElEctrostatic chargEs

1. Electrostatic charges are electric charges that are not moving or
remain stationary at an object.

2. There are two types of electric charges:

a) Positive charge (+) which is proton

b) Negative charge (-) which is electron

3. Electric charges are produced from the friction between two
insulators.

4. When two different materials are rubbed together, electron is
moved from one material to another whereas the proton remains
stationary.

5. Material that receives electron will be negatively-charged whereas
material that losses electron will be positively-charged.

6. The attractive force and the repel force among the electric charges
are known as the electrostatic force.

7. The electroscope is an equipment to detect the presence of
electric charges on an object.

ExamplE of ElEctrostatic in our daily lifE

1. Lightning is an example of a phenomenon related to the
electrostatic charges. The friction between the cloud and the air
transfers electric charges. Lightning happens because of the
attractive forces between the positive charges on the Earth and the
negative charges on the clouds.

2. When someone walks on a carpet,

charges are transferred to the body.

Electrons from the carpet transfer to

the shoes and continue to the body.

When the person holds the doorknob, the body feels the electric

shock because the negative charges move to the doorknob.

solving daily problEms Solution
rElatEd to ElEctrostatic

Problem

Preventing buildings Installing a lightning
from being struck by conductor on top of
lightning. the building to
channel the electrical
charges from the
lightning to the Earth.

Preventing the oil tanker Fixing metal chains at

from catching fire. the back on the tanker

towards the ground for

the flow of the extra

charges to the ground.

Preventing fire at the Touching the body of the car after getting
petrol station. out of the vehicle to discharge the
electrostatic charges from the body.

ElEctric currEnt

1. The electric current is the flow rate of the electric charges through
a conductor.

2. The relationship between the electric charge and electric current:

• Van de Graff generator is an instrument that is able to produce electric
charges or electrostatic charges at its dome.

• When the Van de Graff generator is switched on, the dome becomes
positively charged. Then these charges attract the negative charges or
electrons from the Earth to flow to the dome.

• The flow of electrons causes the deflection of the galvanometer’s needle.
• The deflection of the galvanometer’s needle shows the existence of electric

current.

3. The flow of electric current can be measured by using the
ammeter and the S.I unit for the electric current is ampere (A).

4. The ammeter is connected in series with the electrical
components.

5. Electric current flows from the positive terminal of the dry cell to
the negative terminal while the electron flows from the negative
terminal of the dry cell to the positive terminal.

voltagE

1. Voltage is the potential difference that causes the flow of charges
between two points.

2. Voltage is measured in volt (V) using the voltmeter. The voltmeter
is connected in parallel with the electrical components.

rEsistancE
1. Resistance is the ability of a conductor to resist the flow of the

electrical current through it. The unit for resistance is ohm (Ω).

2. There are two types of resistors:

a) The fixed resistor where the value of the resistance cannot be changed.
b) Variable resistor or rheostat where the value of the resistance can be

changed.

3. The resistance of a resistor depends on:

a) Type of material
b) Length of conductor
c) Diameter
d) Temperature of the conductor

rElationship bEtwEEn currEnt,
voltagE and rEsistancE
1. Ohm’s law states that the electric current flowing in a circuit is

directly proportional to the voltage that goes across it provided
that the temperature and the physical conditions are fixed.

2. The relationship among the three can be stated as follows:

V=IR

The triangle formula to remember Ohm’s law:

V V V
IR IR IR

V= I R I= V R R= V I

4. The following experiment studies the effect of changes in
resistance and voltage on the electric current.
A. Effect of changes in resistance towards current

The higher the resistance, the lower the current that flows through the
circuit.

a) A jockey is placed at the point of 20 cm and the reading on the
ammeter is taken. After that, the ammeter reading of the jockey being
placed at various points are taken.

b) Found that the longer the wire, the reading on the ammeter decreases.
c) This is because the longer the wire, the higher the resistance in the wire.

Therefore, the current that flows in the circuit decreases as the
resistance increases.
d) Current is inversely proportional to resistance is the voltage is constant.

B. The effect of changes in voltage towards current

The higher the voltage, the higher the current flows through the circuit.

a) The circuit is switched on. The ammeter and voltmeter readings for one
dry cell is taken. Then the experiment is repeated using two, three and
four dry cells.

b) This will give a straight graph as shown in the diagram on the below.

c) This graph shows that the current is directly proportional to the voltage.

ExamplE of problEm solving using ohm’s law
The current that flows through the resistor is 0.5 A. If the voltage
that is supplied in the circuit is 1.5 V, what is the resistance value of
the resistor?

Solution

R= V I 0.5 A
= 1.5 V

R= 3 Ω

7.2 FLOW OF CURRENT IN A SERIES
CIRCUIT AND PARALLEL CIRCUIT

ELECTRICAL COMPONENTS AND
SYMBOL

THE DIFFERENCES IN TERMS BETWEEN
SERIES CIRCUIT AND PARALLEL
CIRCUIT

SERIES CIRCUIT PARALLEL CIRCUIT

NUMERICAL PROBLEM RELATED TO CURRENT,VOLTAGE
AND RESISTANCE IN A SERIES CIRCUIT AND PARALLEL

CIRCUIT

7.3
MAGNETISM

• Magnet is a substance that produces magnetic field.
• Magnet attract magnetic substances such as iron, cuprum and nickel.
• Characteristics of a magnet:

(a) Attracts magnetic substances
(b) Has poles that are the north pole and the south pole
(c) Similar poles repel while different poles attract each other

MAGNETIC FIELD

• The magnetic field is the area where the magnetic force can be felt.
• The magnetic field has patterns and directions.
• The magnetic field lines show the magnetic field patterns.

ELECTROMAGNET

An electromagnet is a type of magnet that has temporary
magnetic effect when electric current flow through it.

• When current flows through an iron nail, it becomes an
electromagnet.

• The iron nail can attract small pieces of metal.
• The iron nail will lose its magnetism when the current is

disconnected.
• Its strength increases as the current increases.

• The magnetic field pattern that formed depends
on the shape of the conductor used. The
magnetic line that are produced by a straight
wire and a coiled wire are shaped as concentric
circles.

• The right-hand grip rule determines the direction of
the magnetic field of the straight wire that transports
current.

• Ways to determine the poles of the solenoid magnet
is by observing the direction of the current flow.