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?
คำตอบ
(C)
Iron core
2
What is the unit used to measure power?
คำตอบ
(C)
Watt (W)
3
What is the relationship between voltage and current in a step-up transformer?
คำตอบ
(B)
Voltage increases, current decreases.
4
What does a transformer do?
คำตอบ
(A)
Changes the voltage of an AC supply
5
What is the purpose of the paper cone in a loudspeaker?
คำตอบ
(B)
To vibrate and produce sound waves.
6
What is a compass used for?
คำตอบ
(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?
คำตอบ
(B)
Fleming's left-hand rule.
8
Which of the following increases the magnitude of induced e.m.f.?
คำตอบ
A
C
9
In a transformer, what component links the primary and secondary coils?
คำตอบ
(C)
An iron core.
10
How does the direction of the induced current relate to the motion of the magnet in electromagnetic induction?
คำตอบ
(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?
คำตอบ
(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?
คำตอบ
(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?
คำตอบ
(A)
Step-up
14
What is a characteristic of the Earth's magnetic field?
คำตอบ
(C)
It is constantly changing.
15
What is the role of the coil in a moving coil loudspeaker?
คำตอบ
(B)
To move the paper cone.
16
What are the components of a circuit breaker?
คำตอบ
(A)
An electromagnet and a switch.
17
What is a solenoid?
คำตอบ
(C)
A coil of wire with many turns.
18
In a typical mains supply system, what are voltage changes made?
คำตอบ
(C)
Both increase and decrease
19
What is the function of transformers in a typical power distribution system?
คำตอบ
A
B
20
What are the main components of a basic transformer?
คำตอบ
(B)
A primary coil, a secondary coil, and an iron core
21
In mutual induction, where is the induced e.m.f. generated?
คำตอบ
(B)
In the secondary coil.
22
What happens to a current-carrying wire when placed in a magnetic field?
คำตอบ
(B)
A force acts on the wire.
23
How does a higher frequency impact the operation of a transformer?
คำตอบ
(C)
It can increase the efficiency and power handling capacity.
24
What is the force that can act between poles?
คำตอบ
(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.
คำตอบ
(B)
True
26
What happens to the power loss in a cable when current is reduced?
คำตอบ
(B)
Decreases
27
What is the conventional current direction?
คำตอบ
(C)
Positive to negative
28
What happens to a bar magnet when placed in a strong magnetic field?
คำตอบ
(C)
It will align with the field.
29
What do the magnetic field lines of a bar magnet show?
คำตอบ
(C)
The direction of the field.
30
What is an electromagnet?
คำตอบ
(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?
คำตอบ
(C)
To convert AC to DC
32
What happens to a length of copper wire that has been placed in a magnetic field?
คำตอบ
(B)
It will experience a force if a current is passed through it.
33
What type of electrical energy does an AC generator produce?
คำตอบ
(B)
Alternating current (AC)
34
What is another name for the direction of the magnetic field?
คำตอบ
(A)
Field line.
35
What happens when a magnet is pushed into a coil?
คำตอบ
(A)
An e.m.f. is induced in the coil.
36
What type of material would be attracted to a magnet?
คำตอบ
(B)
Steel.
37
Which factors increase the strength of an electromagnet?
คำตอบ
A
B
C
38
How can the e.m.f. induced in a coil be increased?
คำตอบ
A
B
D
39
What does a transformer do to reduce the current?
คำตอบ
(A)
Increases the voltage
40
What is the main purpose of a magnetic field in an electric motor?
คำตอบ
(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?
คำตอบ
(C)
A transformer.
42
In a step-up transformer, the output voltage is:
คำตอบ
(C)
More than the input voltage.
43
What is the basic function of the commutator in a DC generator?
คำตอบ
(A)
To reverse the current every half cycle.
44
What is used to demonstrate a magnetic field on the earth?
คำตอบ
(A)
A compass.
45
In a moving coil loudspeaker, what is the electrical signal converted into?
คำตอบ
(B)
Mechanical vibrations/sound.
46
If two magnets are placed with like poles next to each other, what will occur?
คำตอบ
(B)
They will repel.
47
What is the primary function of the core in a transformer?
คำตอบ
(C)
To concentrate the magnetic flux.
48
What does Fleming's right-hand rule help determine?
คำตอบ
(A)
The direction of the induced current.
49
What type of electricity is produced by a standard car generator (alternator)?
คำตอบ
(B)
Alternating Current (AC)
50
What does increasing the current do to the magnetic field around a wire?
