Physics for IGCSE & O level - Magnets And Currents (Section 8)
1
What is the definition of a magnetic domain?
Răspuns
(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:
Răspuns
(C)
Watts
7
What can be used to strengthen an electromagnet?
Răspuns
A
B
C
8
What increases the strength of the magnetic field in a coil?
Răspuns
A
B
9
What type of current is used in the primary coil of a transformer?
Răspuns
(B)
Alternating current
10
What happens to the magnetic field of an electromagnet when you increase the current flowing through it?
Răspuns
(C)
The magnetic field becomes stronger
11
Which of the following items can be magnetized?
Răspuns
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?
Răspuns
A
B
C
D
14
What are the main elements that determine the transformer's properties?
Răspuns
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?
Răspuns
(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?
Răspuns
(C)
Primary turns < Secondary turns
18
Which of these factors would affect the strength of a magnetic field produced by a solenoid?
Răspuns
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?
Răspuns
(C)
Isolation
23
What happens to the induced e.m.f. in the second coil when the current in the first coil reverses direction?
Răspuns
(B)
The e.m.f. is reversed.
24
What is the main function of the secondary coil in a transformer?
Răspuns
(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?
Răspuns
(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?
Răspuns
(B)
Decreases
32
How can you reverse the direction of the magnetic field in an electromagnet?
Răspuns
(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?
Răspuns
(B)
To increase the efficiency of the transformer.
35
In a hard disk drive, what is used to write information onto the disk?
Răspuns
(B)
An electromagnet.
36
What is the role of the iron core in an electromagnet?
Răspuns
(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?
Răspuns
(B)
Alternating current (AC).
38
What is the role of the armature in an electric motor?
Răspuns
(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?
Răspuns
(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?
Răspuns
(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?
Răspuns
(A)
e.m.f. is induced.
43
When the coil in a simple generator is vertical, what is the current?
Răspuns
(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?
Răspuns
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?
Răspuns
(A)
To reverse the current's direction.
47
What is induced magnetism?
Răspuns
(C)
Magnetism in a material caused by a nearby magnet.
48
In the context of generators, which type of electrical energy is typically produced?
Răspuns
(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?
