Physics for IGCSE & O level - Magnets And Currents (Section 7)
1
What is the formula for power?
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(B)
P = V * I
2
What is the ideal power input equal to in a transformer?
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(A)
Output power
3
What is the purpose of using high voltage for power transmission?
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A
B
4
What will happen if a piece of iron is placed inside a coil of wire carrying a current?
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(B)
The strength of the magnetic field will increase.
5
What type of current is produced by a simple a.c. generator?
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(B)
Alternating current
6
What does a transformer change?
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(B)
The voltage of a.c. current.
7
Which type of current does an a.c. generator produce?
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(A)
Alternating current
8
What is the cause of the turning effect in an electric motor?
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(A)
The interaction between the coil and a magnetic field.
9
What are the two main types of transformers?
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(C)
Step-up and step-down transformers
10
In a transformer, the efficiency of the device is said to be 100% if:
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(B)
Input power is equal to output power
11
The main reason for using transformers in power transmission is:
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A
B
D
12
What determines the strength of an electromagnet?
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A
B
C
13
What is the effect of increasing the length of a wire on the force it experiences in a magnetic field?
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(A)
The force increases.
14
What happens when you cut a bar magnet in half?
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(B)
You are left with two magnets, each with a north and south pole.
15
Which rule is primarily used to determine the direction of the magnetic field generated around a current-carrying wire?
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(D)
The Right-Hand Grip Rule.
16
What is the relationship between the poles of a magnet and the force between them?
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(A)
Opposite poles attract, and like poles repel.
17
Which of the following is an example of mutual induction?
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(C)
Two coils near each other, with a changing current in one inducing a current in the other.
18
If a magnet is pushed into a coil, what happens?
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(D)
All of the above.
19
What is the purpose of a transformer?
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(B)
To change the voltage of an AC supply.
20
Which of the following are examples of hard magnetic materials?
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B
D
21
What happens to the strength of an electromagnet if the current passing through the wire is increased?
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(B)
The strength increases.
22
What is the definition of the magnetic field lines?
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(B)
The lines showing the direction a compass needle would point.
23
Which of the following is a practical application of a transformer?
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(A)
Changing the voltage of your mobile charger.
24
A transformer is used to ____ a.c. voltage.
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(A)
increase or decrease
25
If a transformer has an input voltage of 100V and an output voltage of 20V, is it a step up or step down transformer?
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(B)
Step-down
26
What is an eddy current?
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(A)
Current induced in a solid conductor by a changing magnetic field.
27
The magnetic field around a straight wire carrying current is in what shape?
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(B)
Concentric circles
28
Which of the following is NOT a factor that affects the strength of an electromagnet?
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(D)
The length of the core.
29
According to Fleming's left-hand rule, which three things are related?
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(A)
Force, Magnetic Field, and Current.
30
What type of transformer is used in a power station for the distribution of electricity?
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(B)
Step-down
31
What type of transformer would be used in a mobile phone charger?
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(B)
Step-down
32
What does the Right-Hand Grip Rule help you determine?
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(B)
The direction of the magnetic field around a current-carrying wire.
33
What does electromagnetic induction produce?
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(B)
An e.m.f.
34
What is the primary use of the circuit breaker?
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(C)
To protect the circuit from overloading.
35
What is the function of the brushes in a simple A.C. generator?
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(C)
To connect the external circuit to the slip rings.
36
What is the function of a relay?
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(B)
To open or close a circuit using a smaller current.
37
What happens to the strength of the magnetic field when the turns of the wire coil in an electromagnet are increased, while keeping the current constant?
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(B)
The strength increases.
38
What is the unit of measurement for the power in an electrical circuit?
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(C)
Watt (W)
39
Which of the following is a main function of a transformer?
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A
D
40
What determines the direction of the induced current in a wire moving through a magnetic field?
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(C)
The direction of the magnetic field and the direction of the wire's movement.
41
If a transformer has a turns ratio of 1:10, what will happen to the current?
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(B)
It will decrease by a factor of 10
42
What would cause the e.m.f. to change in an induction coil?
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A
B
43
What is an advantage of using electromagnets in motors?
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(C)
The electromagnet can be turned on and off
44
What is the function of the recording head in a tape recorder?
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(C)
To magnetize the tape according to the signal.
45
In a moving coil meter, what is indicated by the scale reading?
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(B)
The amount of current flowing.
46
What happens to the magnetic field in a wire if the direction of the current is reversed?
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(C)
The magnetic field reverses direction.
47
Which type of magnetic materials retain their magnetism for long periods?
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(B)
Hard
48
What are the properties of magnetic field lines?
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A
B
C
D
49
What is the difference between a hard and a soft magnetic material?
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(C)
Hard materials retain their magnetism; soft materials lose it easily.
50
A transformer is designed to have a secondary voltage of 24V and a turns ratio of 1:4. What is the primary voltage?
