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