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