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Physics for IGCSE & O level - Magnets And Currents (Section 4)

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