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