Physics for IGCSE & O level - Magnets And Currents (Section 1)
1
What type of material is a hard drive made of?
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(B)
A layer of a metal made by coating with an alloy like Iron Oxide
2
In the context of power transmission, what is the main purpose of high voltages?
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(B)
To reduce the power loss
3
What happens to the current when voltage is stepped down in a transformer?
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(A)
Increases
4
What is the primary function of a transformer in an electrical circuit?
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(C)
To change the voltage level of an AC circuit.
5
What happens to the voltage in a step-up transformer?
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(A)
It increases.
6
What is the relationship between frequency and the number of poles in a generator?
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(B)
They are directly proportional.
7
What causes the coil in an electric motor to turn?
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(B)
The interaction of the current in the coil with the magnetic field.
8
What is the name given to the region around a magnet where its effects can be felt?
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(A)
Magnetic field
9
What is the relationship between the number of turns and the voltage in a transformer?
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(A)
Directly proportional
10
How is a voltage induced in a wire?
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(A)
By passing a wire through a magnetic field.
11
What type of electrical signal does a typical audio amplifier take as input?
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(B)
Alternating current (AC).
12
In a transformer, what does the ratio of turns in the primary and secondary coils determine?
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(A)
The voltage ratio.
13
A simple transformer works by:
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(B)
Mutual induction
14
What will happen to iron filings near a magnet?
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(C)
They will align with the magnetic field.
15
How are the strength and direction of a magnetic field related?
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(D)
Both strength and direction can affect each other.
16
In electromagnetic induction, what creates the induced current?
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(A)
A changing magnetic field.
17
What principle is used by an induction hob (cooktop)?
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(A)
Electromagnetic induction
18
What happens to the current in a step-up transformer?
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(B)
Decreases
19
What is the relationship between the distance of magnetic poles and the force between them?
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(C)
As distance decreases, force increases.
20
What is the function of the armature in a DC motor?
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(B)
To carry the current and experience torque.
21
What would happen if you connected a DC power supply to the primary side of a transformer designed for AC?
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(D)
The transformer would likely be damaged or overheat.
22
What causes a ring of voltage along the cable and a loss of power?
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(D)
All of the above
23
What happens when a bar magnet is moved away from a coil?
คำตอบ
(A)
An e.m.f. is induced in the coil.
24
In a transformer, which coil receives the initial power supply?
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(A)
Primary Coil
25
In a step-up transformer, if the primary voltage is 120V and the secondary voltage is 240V, what is the turns ratio?
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(B)
1:2
26
What factors affect the force on a current-carrying wire in a magnetic field?
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A
B
C
27
What are the main parts of a simple AC generator?
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(A)
Coil, slip rings, magnets
28
Power for the a.c. mains is generated in power stations, transmitted (sent) through long-distance cables, and then distributed to consumers. What is the next step in the process?
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(B)
Distribution
29
What type of current is used in the mains electricity supply?
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(B)
AC
30
Which of the following factors can increase the e.m.f. induced in a wire?
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A
B
C
31
What is the main use of a transformer in power distribution?
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(B)
To reduce voltage for household use.
32
What type of energy transformation occurs in an electric motor?
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(A)
Electrical to mechanical.
33
What are the main components of a simple transformer?
คำตอบ
A
B
C
34
Which of the following best describes the relationship between voltage and current in an ideal transformer?
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(B)
Voltage and current are inversely proportional.
35
What is a hard disk made of?
คำตอบ
(A)
A magnetic material.
36
What is the purpose of a step-down transformer?
คำตอบ
(B)
To decrease the voltage.
37
In electromagnetic induction, when is the induced e.m.f. greatest?
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(B)
When the magnet is moving rapidly.
38
What is the function of a commutator in a DC motor?
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(B)
To reverse the current direction every half cycle.
39
What is the formula for calculating the voltage across the input coil?
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(B)
input voltage/output voltage = turns on output coil/ turns on input coil
40
In power transmission, what is done to the voltage before the energy is sent over long distances?
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(A)
Increased
41
What happens to the direction of the current in a generator as the coil rotates?
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(B)
The direction reverses periodically.
42
Which factor does NOT directly influence the output voltage of an AC generator?
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(D)
The color of the insulation on the wires.
43
What is the turning effect in an electric motor called?
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(C)
Torque
44
What kind of core is usually used in a transformer?
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(C)
Iron core
45
How can the direction of the magnetic field produced by a current-carrying coil be determined?
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(C)
Using Fleming's left-hand rule
46
How does the moving coil loudspeaker produce sound?
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(C)
By vibrating the paper cone.
47
What increases the turning effect on the coil in an electric motor?
คำตอบ
A
B
C
48
What happens to the magnetic field lines when the magnetic field lines are close together?
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(B)
The field is stronger
49
How is the output of an AC generator often represented?
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(C)
A sine wave.
50
What is the principle of operation for an electric generator?
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(A)
Conversion of mechanical energy to electrical energy via electromagnetic induction.
