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