1. Motion, forces and energy

1.1 Physical quantities and measurement techniques

1.2 Motion

1.3 Mass and weight

1.4 Density

1.5.1 Effects of forces

1.5.2 Turning effect of forces

1.5.3 Centre of gravity

1.6 Momentum

1.7.1 Energy

1.7.2 Work

1.7.3 Energy resources

1.7.4 Power

1.8 Pressure

2. Thermal physics

2.1.1 States of matter

2.1.2 Particle model

2.1.3 Gases and the absolute scale of temperature

2.2.1 Thermal expansion of solids, liquids and gases

2.2.2 Specific heat capacity

2.2.3 Melting, boiling and evaporation

2.3.1 Conduction

2.3.2 Convection

2.3.3 Radiation

2.3.4 Consequences of thermal energy transfer

3. Waves

3.1 General properties of waves

3.2.1 Reflection of light

3.2.2 Refraction of light

3.2.3 Thin lenses

3.2.4 Dispersion of light

3.3 Electromagnetic spectrum

3.4 Sound

4. Electricity and magnetism

4.1 Simple phenomena of magnetism

4.2.1 Electric charge

4.2.2 Electric current

4.2.3 Electromotive force and potential difference

4.2.4 Resistance

4.2.5 Electrical energy and electrical power

4.3.1 Circuit diagrams and circuit components

4.3.2 Series and parallel circuits

4.3.3 Action and use of circuit components

4.4 Electrical safety

4.5.1 Electromagnetic induction

4.5.2 The a.c. generator

4.5.3 Magnetic effect of a current

4.5.4 Force on a current-carrying conductor

4.5.5 The d.c. motor

4.5.6 The transformer

5. Nuclear physics

5.1.1 The atom

5.1.2 The nucleus

5.2.1 Detection of radioactivity

5.2.2 The three types of nuclear emission

5.2.3 Radioactive decay

5.2.4 Half-life

5.2.5 Safety precautions

6. Space physics

6.1.1 The Earth

6.1.2 The Solar System

6.2.1 The Sun as a star

6.2.2 Stars

6.2.3 The Universe

IGCSE Physics 4.5.5 The d.c. motor Question Bank

[Maximum number: 1]

Which component forms part of a d.c. motor but not a simple moving coil a.c. generator?

the coil

the brushes

the magnet

the split-ring commutator

[Maximum number: 1]

A class is designing a d.c. motor. To achieve a greater turning effect, three suggestions are made.

1 Have a larger current in the coil of the motor.
2 Have a stronger magnet in the motor.
3 Put a larger number of turns on the coil.
Which suggestions will help to increase the turning effect?

1, 2 and 3

1 and 2 only

1 and 3 only

2 and 3 only

[Maximum number: 1]

What is the function of the split-ring commutator in an electric motor with a single rotating coil?

to enable the motor to function with an a.c. source

to reverse the current in the coil once every revolution

to reverse the current in the coil whenever its plane becomes perpendicular to the magnetic field

to reverse the current in the coil whenever its plane is parallel with the magnetic field

[Maximum number: 1]

A simple d.c. electric motor is fitted with a coil that rotates in a magnetic field. A commutator connects the power supply to the coil.

What is the purpose of the commutator?

It converts a.c. into d.c. in the coil.

It prevents the current from becoming too great, because the coil has a low resistance.

It reverses the direction of the current in the coil after every $180^{\circ}$ rotation of the coil.

It switches the current off momentarily after every $90^{\circ}$ rotation of the coil.

[Maximum number: 1]

In which device is a split-ring commutator used, and what is its purpose?

device

purpose

a.c. generator

to change the direction of the
current in the coil as it turns

a.c. generator

to change the output current
from d.c. into a.c.

d.c. motor

to change the direction of the
current in the coil as it turns

d.c. motor

to change the input current
from a.c. into d.c.

[Maximum number: 1]

Which device uses a split-ring commutator?

a d.c. motor

a relay

a transformer

an a.c. generator

[Maximum number: 1]

The diagram shows a coil of wire between the poles of a magnet.

The coil consists of 20 turns of insulated wire.
The coil is connected to a variable resistor and a power supply.
How can the turning effect on the coil be increased?

by moving the poles of the magnet closer to the coil

by reducing the number of turns on the coil while keeping the current constant

by increasing the resistance of the variable resistor

by reversing the terminals of the power supply

[Maximum number: 1]

What is the purpose of the commutator in a d.c. electric motor?

to control the speed at which the motor rotates

to reverse the direction of the voltage across the power supply every half-turn

to reverse the direction of the current in the motor coil every half-turn

to reverse the direction of spin of the motor coil every half-turn

[Maximum number: 1]

Diagram 1 shows a coil of wire P between the poles of a magnet. The ends of coil P are connected to a battery by slip rings.

Diagram 2 shows a coil of wire Q between the poles of a different magnet. The ends of coil Q are connected to a battery by a split-ring commutator.

diagram 1

diagram 2

What happens to coils P and Q ?

coil P

coil Q

continuously turns
anticlockwise

makes one quarter turn
anticlockwise then stops

continuously turns
clockwise

makes one quarter turn
clockwise then stops

makes one quarter turn
anticlockwise then stops

continuously turns
anticlockwise

makes one quarter turn
clockwise then stops

continuously turns
clockwise

(a)

Fig. 8.3 shows a simple direct current (d.c.) electric motor with a split-ring commutator.

Fig. 8.3

[ 6 ]

(i)

State and explain the direction of rotation of the coil as seen from point X .
statement
explanation

[ 3 ]

(ii)

The coil rotates through $90^{\circ}$ from the position shown.

State what happens to the moment in this position.

[ 1 ]

(iii)

The coil is rotated through $180^{\circ}$ from the position shown. By considering the forces on the coil, explain how the split-ring commutator enables the motor to turn continuously.

[ 2 ]

0 selected

Question 31

Question 31

Question 34

Question 35

Question 35

Question 36

Question 36

Question 36

Question 36

Question 8

Question 8(b)

Question 8(b)(i)

Question 8(b)(ii)

Question 8(b)(iii)