Physics for IGCSE & O level - Magnets And Currents (Section 4)
1
What happens during transmission?
2
What is a disadvantage of using a DC power supply with an AC transformer?
3
If the number of turns in the primary coil of a transformer is increased, what will happen to the induced voltage?
4
What type of material is most readily magnetized?
Отвечать(C)
A soft magnetic material.
5
How does a transformer work on the principle of mutual induction?
Отвечать(A)
A changing current in the primary coil induces a current in the secondary coil.
6
What is the purpose of the iron core in a transformer?
Отвечать(A)
To increase the efficiency of the transformer by channeling the magnetic flux.
7
Which pole is located on the Earth?
8
In an AC generator, what causes the current to reverse direction?
Отвечать(A)
The rotation of the coil.
9
What is the purpose of a magnetic relay?
10
What is used to control the switch in a relay?
11
What does the core of a transformer usually made of?
12
In a circuit breaker, the electromagnet's strength is...
Отвечать(A)
Used to open the circuit.
13
What is the difference between magnetic poles?
14
What rule is used to determine the direction of the magnetic field around a current-carrying wire?
15
How do step-down transformers affect the voltage?
16
What is the effect of the core in a transformer regarding the magnetic field?
17
Which of the following is used in AC generator, but NOT in DC generator?
18
What is the force between two unlike poles?
19
What do the brushes in an electric motor or generator do?
Отвечать(B)
They make contact with the rotating parts to conduct current.
20
How is the direction of the force on a current-carrying wire in a magnetic field predicted?
Отвечать(B)
Fleming's left hand rule.
21
High-voltage transmission cables are:
22
What is the role of the slip rings?
Отвечать(C)
To connect the coil to the external circuit.
23
Which of the following will demagnetize a magnet?
24
What happens to the current when voltage is increased by a transformer?
25
What happens when a bar magnet is dipped in iron filings?
26
What are the key features of the magnetic field around a wire carrying a current?
Отвечать(A)
The magnetic field lines are circular.
27
What component in a generator ensures the current direction reverses?
28
In a current-carrying wire, the field direction depends on...
Отвечать(C)
the direction of the current.
29
Which law describes the direction of induced current?
30
What is the formula to calculate power in terms of voltage and current?
31
What happens to the power if no energy is wasted in a transformer?
Отвечать(A)
Power input = power output
32
What is the role of a moving coil loudspeaker?
Отвечать(B)
To convert electrical signals to sound.
33
What type of core is most frequently used in transformers?
34
What is a key factor in the efficiency of a well-designed transformer?
Отвечать(A)
The type of core material used
35
What can be used to see the shape of the magnetic field?
36
What is the role of the armature in a motor?
Отвечать(C)
To rotate due to the force from magnets
37
If the input voltage to a transformer is 10V and the output voltage is 5V, what is the nature of the transformer?
38
In a moving coil loudspeaker, what causes the coil to move?
Отвечать(C)
The changing current in the coil and interaction with the magnetic field.
39
What type of materials can be magnetized?
40
If a transformer has a turns ratio of 1:4, and the input voltage is 12V, what is the output voltage?
41
What are the uses of an electromagnet?
42
What is the main difference between a generator and a motor?
Отвечать(B)
A motor converts electrical to mechanical; a generator does the reverse.
43
What is the unit for measuring the frequency of AC?
44
Which of the following are applications of electromagnets?
45
What component of the transformer is used to minimize the energy loss due to heating effects?
46
Which of the following is the main advantage of using a.c. in power transmission?
Отвечать(B)
It can be easily stepped up or down
47
What causes eddy currents in a conductor?
Отвечать(B)
A changing magnetic field.
48
Which of the following are magnetic materials?
49
What force is responsible for the movement of the coil in an electric motor?
50
What does an appliance with a power output of 1000W deliver energy at the rate of?
