Physics for IGCSE & O level - Magnets And Currents (Section 8)
1
What is the definition of a magnetic domain?
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(B)
A small region of a magnetic material where the magnetic fields of the atoms are aligned.
2
Which of the following statements best describes the role of transformers in the power grid?
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(C)
They change the voltage levels of AC power.
3
What is a solenoid?
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(C)
A coil of wire.
4
What is the function of the magnetic field?
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(B)
To exert a force on moving electric charges.
5
What factors increase the strength of a magnetic field in an electromagnet?
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A
B
6
The units of electrical power are:
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(C)
Watts
7
What can be used to strengthen an electromagnet?
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A
B
C
8
What increases the strength of the magnetic field in a coil?
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A
B
9
What type of current is used in the primary coil of a transformer?
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(B)
Alternating current
10
What happens to the magnetic field of an electromagnet when you increase the current flowing through it?
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(C)
The magnetic field becomes stronger
11
Which of the following items can be magnetized?
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A
C
12
Which law explains the working of a transformer?
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(B)
Faraday's law of electromagnetic induction
13
What are the losses that affect the efficiency of a transformer?
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A
B
C
D
14
What are the main elements that determine the transformer's properties?
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A
B
D
15
Which rule helps to determine the direction of the force on a current-carrying conductor placed in a magnetic field?
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(B)
Fleming's Left-Hand Rule
16
How is the direction of the magnetic field defined?
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(B)
The direction a compass needle will point
17
In a step-up transformer, what is the relationship between the number of turns in the primary and secondary coils?
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(C)
Primary turns < Secondary turns
18
Which of these factors would affect the strength of a magnetic field produced by a solenoid?
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B
C
D
19
How is sound produced by a moving-coil loudspeaker?
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(C)
By the vibration of the cone.
20
What is the term for the process of removing magnetic properties from a material?
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(B)
Demagnetization.
21
In which device is an electromagnet typically used?
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(C)
A loudspeaker.
22
What type of transformer is used to safely isolate a circuit from the mains supply?
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(C)
Isolation
23
What happens to the induced e.m.f. in the second coil when the current in the first coil reverses direction?
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(B)
The e.m.f. is reversed.
24
What is the main function of the secondary coil in a transformer?
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(C)
To supply electrical energy.
25
What is the effect of increasing the number of turns of wire on a coil in an electromagnet?
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(B)
The magnetic field increases.
26
What is meant by 'turns ratio' of a transformer?
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(B)
Ratio of primary coil turns to secondary coil turns
27
What is the direction of the magnetic field outside of a bar magnet?
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(A)
From the north pole to the south pole.
28
In which direction does the current flow in a simple A.C. generator?
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(B)
Reverses direction periodically.
29
If the number of turns in the primary coil of a transformer is increased, while keeping the number of turns in the secondary coil constant, what will happen to the output voltage?
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(B)
Decrease
30
What are the main functions of a step up transformer?
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(C)
Increase the voltage
31
What happens to the current in the secondary coil of a step-up transformer?
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(B)
Decreases
32
How can you reverse the direction of the magnetic field in an electromagnet?
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(C)
Reverse the direction of the current.
33
What is the benefit of using laminated core in transformers?
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(A)
To reduce eddy current losses
34
What is the purpose of the iron core in a transformer?
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(B)
To increase the efficiency of the transformer.
35
In a hard disk drive, what is used to write information onto the disk?
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(B)
An electromagnet.
36
What is the role of the iron core in an electromagnet?
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(B)
To increase the strength of the magnetic field.
37
In a moving-coil loudspeaker, what type of current does the amplifier send to the coil?
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(B)
Alternating current (AC).
38
What is the role of the armature in an electric motor?
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(B)
To rotate in the magnetic field.
39
What happens to the direction of the magnetic field when the direction of the current in a wire is reversed?
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(C)
The field reverses direction.
40
Which statement best describes the magnetic field lines around a bar magnet?
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(C)
They form closed loops, originating from the North pole and going to the South pole.
41
What happens to the force on a current-carrying wire in a magnetic field if the current is doubled?
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(B)
The force is doubled.
42
What happens to the amount of e.m.f. in the second coil if the current in the first coil is switched off?
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(A)
e.m.f. is induced.
43
When the coil in a simple generator is vertical, what is the current?
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(B)
Zero
44
A transformer with a turns ratio of 1:5 is connected to a 120 V AC supply. Which of the following statements is correct about the output voltage?
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A
C
45
What happens if two north poles of magnets are brought together?
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(B)
They will repel each other.
46
What is the function of a commutator in an electric motor?
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(A)
To reverse the current's direction.
47
What is induced magnetism?
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(C)
Magnetism in a material caused by a nearby magnet.
48
In the context of generators, which type of electrical energy is typically produced?
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(B)
Alternating Current (AC)
49
What is the purpose of a circuit breaker?
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(C)
To switch off the current in a circuit when it is too high.
50
What factors contribute to power losses in a transformer?
