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