Physics for IGCSE & O level - Magnets And Currents (Section 11)
1
What is the relationship between the primary and secondary coils in a transformer?
Απάντηση
(A)
They are electrically isolated but magnetically linked.
2
What is the role of a core material made of iron within an electromagnet?
Απάντηση
(C)
To increase the strength of the magnetic field.
3
What are the functions of the different parts of a transformer?
Απάντηση
A
C
4
What is the relationship between the coil's position and the a.c. output in a simple generator?
Απάντηση
(B)
The a.c. output varies with the coil's position.
5
What is the name of the rule to determine the direction of the induced current?
Απάντηση
(A)
Fleming's right-hand rule
6
What is the function of a rectifier in a car alternator?
Απάντηση
(A)
To convert AC to DC.
7
What is the force between the poles of two magnets?
Απάντηση
(C)
Dependent on the type of poles.
8
What is the key operating principle in an electric motor?
Απάντηση
(C)
The force on a current-carrying wire in a magnetic field.
9
What is the relationship between magnetism and electricity?
Απάντηση
(B)
Electricity can produce magnetism, and magnetism can produce electricity.
10
How can eddy current losses be minimized in a transformer?
Απάντηση
(C)
Laminating the core
11
What happens when you cut a bar magnet in half lengthwise?
Απάντηση
(B)
You are left with two magnets, each with a north and south pole.
12
Which of the following materials is suitable for the core of an electromagnet?
Απάντηση
(C)
Iron
13
Which of the following is a practical application of electromagnets?
Απάντηση
(C)
An electric motor.
14
What happens to the strength of the magnetic field created by a coil of wire (solenoid) if the number of coils is increased?
Απάντηση
(A)
The strength increases.
15
How can the force on a current-carrying wire in a magnetic field be increased?
Απάντηση
A
B
C
16
What determines whether a transformer is step-up or step-down?
Απάντηση
(C)
The ratio of turns in the primary and secondary coils.
17
What does a turns ratio of 2:1 indicate about a transformer?
Απάντηση
(A)
Output voltage is twice the input voltage
18
What increases the frequency of a.c. motor?
Απάντηση
(D)
Increasing the motor's rotary speed.
19
In a transformer, if the voltage is increased, then the current will:
Απάντηση
(B)
decrease
20
If the primary coil has 100 turns and the secondary has 200 turns, is this a step up or a step down transformer?
Απάντηση
(A)
Step-up.
21
In a transformer, what does the core material primarily affect?
Απάντηση
(C)
The efficiency of the transformer
22
Which of the following is the best description of a magnetic domain?
Απάντηση
(B)
A small region of a magnetic material where atoms are aligned.
23
What is the primary purpose of the iron core in an electromagnet?
Απάντηση
(B)
To increase the strength of the magnetic field.
24
What material is commonly used to make the core of an electromagnet?
Απάντηση
(B)
Iron
25
How does the electric current flow in a direct current (DC) generator?
Απάντηση
(A)
In a single direction.
26
The core of the transformer is made of?
Απάντηση
(A)
Magnetic material
27
What is the role of the recording head in a tape recorder?
Απάντηση
(B)
To convert electrical signals to magnetic signals.
28
What type of current produces a magnetic field?
Απάντηση
B
C
29
What factors contribute to energy losses in a transformer?
Απάντηση
A
B
C
D
30
What is the purpose of a relay?
Απάντηση
(B)
To automatically open or close an electrical circuit
31
If the current flows in the same direction through the coil, what can happen?
Απάντηση
(B)
The coil will turn a small amount, and then stop.
32
What is the direction of a magnetic field line around a wire carrying current?
Απάντηση
(D)
In a circular pattern around the wire.
33
What is the relationship between voltage, current, and power in a transformer?
Απάντηση
(D)
Power remains constant if there is no energy loss
34
In which way is a solenoid different from a simple wire?
Απάντηση
(B)
It is a coil of wire.
35
What happens when like poles of two magnets are brought close together?
Απάντηση
(B)
They will repel.
36
The direction of the magnetic field produced by a current can be determined by using which rule?
Απάντηση
(A)
Fleming's right-hand rule
37
Which of the following is a common use of an electromagnet?
Απάντηση
(D)
In a door bell
38
In a transformer, the ratio of the number of turns in the primary coil to the number of turns in the secondary coil determines:
Απάντηση
(B)
The voltage ratio.
39
What principle is used in an induction hob?
Απάντηση
(D)
Eddy Currents.
40
What is the unit for measuring the current?
Απάντηση
(B)
Ampere
41
Which of the following is an example of a magnetic material?
Απάντηση
(C)
Iron
42
In which direction does the Earth's magnetic field point in Canada?
Απάντηση
(A)
North
43
Which factors can increase the turning effect on the coil in a simple generator?
Απάντηση
A
B
C
44
What is the main purpose of a transformer?
Απάντηση
(B)
To change the voltage of an alternating current
45
What is the name of the instrument used to measure the force in a coil in a moving-coil meter?
Απάντηση
(C)
A moving-coil meter
46
What principle allows a transformer to work?
Απάντηση
(A)
Electromagnetic induction
47
How does the Earth’s magnetic field affect a compass?
Απάντηση
(A)
It causes the compass needle to point North.
48
Why are step-up transformers used in power transmission?
Απάντηση
(A)
To decrease the current and reduce power loss.
49
If a transformer has a primary voltage of 120 V, a secondary voltage of 24 V, and the primary coil has 1000 turns, how many turns does the secondary coil have?
