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