Physics for IGCSE & O level - Magnets And Currents (Section 5)
1
What is the effect of eddy currents?
2
What is the basic function of a magnetic relay?
إجابة(B)
To allow a small current to control a larger one.
3
Which of the following are reasons why a.c. is used for the mains?
4
If an electric motor stalls, what is likely to happen?
إجابة(C)
The current drawn by the motor will increase dramatically.
5
What is the role of an amplifier in a loudspeaker system?
إجابة(B)
To increase the power of the electrical signal.
6
What is the main reason for using step-up transformers in the transmission of electricity over long distances?
7
What is the relationship between the number of turns on the primary and secondary coils of a transformer and the voltages?
8
What is the magnetic field around a wire carrying current?
إجابة(B)
Circular around the wire.
9
What is the main function of transformers in the power grid?
10
How is the direction of the force on a current-carrying wire in a magnetic field determined?
إجابة(C)
Using Fleming's left-hand rule.
11
What is the impact of eddy currents?
12
In a generator, what is the purpose of the magnets?
إجابة(A)
To create the changing magnetic field.
13
If energy is wasted, the power delivered by the output coil is:
إجابة(C)
The same as the power supplied to the input coil.
14
إجابة(A)
Circulating currents induced within a conductor by a changing magnetic field.
15
How can the induced e.m.f. be increased?
16
If the input voltage is 12 V and the output voltage is 24 V, what is the ratio of turns on the output coil to the turns on the input coil?
17
What does Fleming's Left-Hand Rule describe?
إجابة(B)
The direction of force on a current-carrying wire in a magnetic field.
18
How does a circuit breaker protect a circuit?
إجابة(C)
By automatically opening when current is too high.
19
Which component is found in both AC and DC generators?
20
Which type of generator supplies a direct current?
21
What does 'demagnetized' mean?
إجابة(A)
The loss of magnetic properties.
22
What is the ratio between the voltage and the turns on both sides of the transformer?
23
What are the two main types of transformers?
24
What does the turns ratio of a transformer influence?
25
What is meant by "step-up" in the context of a transformer?
26
What happens when the current increases?
27
In calculating power loss in a cable, which parameter is the main source of the loss?
28
In a transformer, what causes the voltage to change from the primary to the secondary?
إجابة(C)
The turns ratio of the coils.
29
What is another term for the magnetic north-seeking pole?
31
What will increase the strength of the magnetic field of an electromagnet?
32
In the primary coil of a transformer, what kind of current is used?
33
Which of the following components are used in a circuit breaker?
34
In the context of power transmission, what is typically transmitted across long distances?
إجابة(B)
High voltage, low current
35
Which factor does NOT affect the magnitude of the e.m.f. induced in a coil?
36
What causes the Earth's magnetic field?
إجابة(A)
Electric currents in the Earth's core.
37
What happens if the current direction in a coil is reversed?
إجابة(B)
The polarity of the magnetic field reverses.
38
What happens to the force between magnetic poles as they get closer?
39
What is a key characteristic of a simple generator?
إجابة(B)
It produces an AC output.
40
What does the term "turns ratio" refer to in a transformer?
إجابة(B)
The ratio of the number of turns in the primary coil to the number of turns in the secondary coil.
41
What is the use of a solenoid?
إجابة(B)
Creating a uniform magnetic field.
42
What type of current is produced by a car alternator?
43
What will happen if the two north poles of two magnets are placed close to each other?
44
What is the primary characteristic of a permanent magnet?
إجابة(A)
It always has a north and south pole.
45
In which direction does the magnetic field around a wire carrying current travel?
إجابة(B)
Perpendicular to the wire.
46
What principle is used in the moving-coil loudspeaker?
إجابة(A)
Turning effect in a coil.
47
What happens when the secondary circuit of a transformer is open?
إجابة(B)
Primary current decreases to almost zero.
48
What is the purpose of the core in a transformer?
إجابة(C)
To provide a path for the magnetic flux
49
What is the purpose of the spring holding the meter?
إجابة(B)
To provide a force opposite to the force.
50
What is the key application for the Fleming's Left-Hand Rule?
إجابة(B)
To determine the force on a wire in a magnetic field.
