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