Physics for IGCSE & O level - Magnets And Currents (Section 3)
1
What type of core is typically used to increase the strength of an electromagnet?
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(C)
Iron core
2
What is the unit used to measure power?
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(C)
Watt (W)
3
What is the relationship between voltage and current in a step-up transformer?
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(B)
Voltage increases, current decreases.
4
What does a transformer do?
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(A)
Changes the voltage of an AC supply
5
What is the purpose of the paper cone in a loudspeaker?
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(B)
To vibrate and produce sound waves.
6
What is a compass used for?
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(C)
To detect magnetic fields.
7
What is the rule used for finding the force's direction on a current-carrying wire in a magnetic field?
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(B)
Fleming's left-hand rule.
8
Which of the following increases the magnitude of induced e.m.f.?
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A
C
9
In a transformer, what component links the primary and secondary coils?
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(C)
An iron core.
10
How does the direction of the induced current relate to the motion of the magnet in electromagnetic induction?
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(B)
The current's direction opposes the magnet's motion.
11
What will happen if the speed of rotation in a simple AC generator is increased?
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(B)
The frequency of the AC output will increase.
12
In a transformer, if the secondary coil has more turns than the primary coil, what happens to the voltage?
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(A)
The voltage increases.
13
If the primary coil has 100 turns and the secondary coil has 200 turns, is this a step-up or step-down transformer?
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(A)
Step-up
14
What is a characteristic of the Earth's magnetic field?
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(C)
It is constantly changing.
15
What is the role of the coil in a moving coil loudspeaker?
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(B)
To move the paper cone.
16
What are the components of a circuit breaker?
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(A)
An electromagnet and a switch.
17
What is a solenoid?
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(C)
A coil of wire with many turns.
18
In a typical mains supply system, what are voltage changes made?
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(C)
Both increase and decrease
19
What is the function of transformers in a typical power distribution system?
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A
B
20
What are the main components of a basic transformer?
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(B)
A primary coil, a secondary coil, and an iron core
21
In mutual induction, where is the induced e.m.f. generated?
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(B)
In the secondary coil.
22
What happens to a current-carrying wire when placed in a magnetic field?
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(B)
A force acts on the wire.
23
How does a higher frequency impact the operation of a transformer?
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(C)
It can increase the efficiency and power handling capacity.
24
What is the force that can act between poles?
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(A)
Magnetic
25
A transformer has a turns ratio of 2. The same ratio links the voltages: Vp/Vs = 12/6 = 1. Put in words, the output coil has the same number of turns of the input coil; so the output voltage is twice the input voltage.
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(B)
True
26
What happens to the power loss in a cable when current is reduced?
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(B)
Decreases
27
What is the conventional current direction?
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(C)
Positive to negative
28
What happens to a bar magnet when placed in a strong magnetic field?
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(C)
It will align with the field.
29
What do the magnetic field lines of a bar magnet show?
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(C)
The direction of the field.
30
What is an electromagnet?
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(A)
A magnet that produces a magnetic field when an electric current flows through it.
31
What is the main function of a rectifier circuit?
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(C)
To convert AC to DC
32
What happens to a length of copper wire that has been placed in a magnetic field?
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(B)
It will experience a force if a current is passed through it.
33
What type of electrical energy does an AC generator produce?
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(B)
Alternating current (AC)
34
What is another name for the direction of the magnetic field?
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(A)
Field line.
35
What happens when a magnet is pushed into a coil?
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(A)
An e.m.f. is induced in the coil.
36
What type of material would be attracted to a magnet?
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(B)
Steel.
37
Which factors increase the strength of an electromagnet?
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A
B
C
38
How can the e.m.f. induced in a coil be increased?
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A
B
D
39
What does a transformer do to reduce the current?
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(A)
Increases the voltage
40
What is the main purpose of a magnetic field in an electric motor?
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(C)
To provide the force that causes rotation.
41
What type of device can be used to step up or step down voltage in an AC circuit?
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(C)
A transformer.
42
In a step-up transformer, the output voltage is:
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(C)
More than the input voltage.
43
What is the basic function of the commutator in a DC generator?
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(A)
To reverse the current every half cycle.
44
What is used to demonstrate a magnetic field on the earth?
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(A)
A compass.
45
In a moving coil loudspeaker, what is the electrical signal converted into?
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(B)
Mechanical vibrations/sound.
46
If two magnets are placed with like poles next to each other, what will occur?
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(B)
They will repel.
47
What is the primary function of the core in a transformer?
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(C)
To concentrate the magnetic flux.
48
What does Fleming's right-hand rule help determine?
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(A)
The direction of the induced current.
49
What type of electricity is produced by a standard car generator (alternator)?
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(B)
Alternating Current (AC)
50
What does increasing the current do to the magnetic field around a wire?
