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