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