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