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