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Physics for IGCSE & O level - Magnets And Currents (Section 6)

1
What causes the force on the coil in a motor?
Answer
(B)
The current flowing through the coil in a magnetic field.
2
What will happen in the primary coil of a transformer if the secondary coil circuit is open?
Answer
(D)
The current in the primary coil will decrease
3
What is the unit for current?
Answer
(B)
Ampere
4
How does an iron core affect the strength of a magnetic field in an electromagnet?
Answer
(B)
It increases the strength.
5
In a moving coil meter, what is the purpose of the spring?
Answer
(B)
To resist the force on the coil.
6
What does an induced e.m.f. cause?
Answer
(B)
A current to flow.
7
What is a key characteristic of a temporary magnet?
Answer
(B)
It loses its magnetism easily.
8
What is the purpose of the armature in an electric motor?
Answer
(B)
To rotate and generate a magnetic field.
9
A transformer's efficiency is the ratio of
Answer
(C)
output power to input power
10
Which of the following best describes the function of a relay?
Answer
(C)
To switch a circuit on or off using a smaller current.
11
What is the name of the effect that is present when a magnet is brought near an unmagnetized piece of steel and it is turned into a magnet?
Answer
(B)
Magnetic induction
12
In an electromagnet, the magnetic field is produced by:
Answer
(B)
the current flowing through the coil.
13
What happens to the power transmitted by a transformer if the voltage is increased?
Answer
(C)
Power remains constant
14
What happens if the number of turns on the secondary coil is greater than the number of turns on the primary coil of a transformer?
Answer
(B)
The voltage is stepped up.
15
In a transformer, if the primary voltage is 120V, and the secondary voltage is 12V, what type of transformer is it?
Answer
(B)
Step-down
16
What is the result of placing a magnet near a piece of iron?
Answer
(A)
The iron becomes magnetized.
17
What are the key components needed to make a simple transformer?
Answer
A
B
18
What is the key principle behind the operation of an electric motor?
Answer
(A)
A current-carrying coil experiences a force in a magnetic field.
19
What is the primary reason for transmitting electricity at high voltage?
Answer
(B)
To reduce losses due to resistance
20
What is the purpose of the magnetic field lines?
Answer
(A)
To show the shape and direction of the magnetic field.
21
In a transformer, the ratio of the input voltage to the output voltage is equal to the ratio of:
Answer
(A)
turns on output coil to turns on input coil
22
What is the relationship between current and the number of turns in a transformer?
Answer
(B)
They are inversely proportional
23
What is required to produce a turning effect?
Answer
(C)
A coil, a magnet, and current flow.
24
If the voltage is increased by a factor of 10, how does the current change, assuming no losses?
Answer
(B)
Decreases by a factor of 10
25
What is the effect of reversing the current direction in a solenoid?
Answer
(C)
The direction of the magnetic field reverses.
26
In which part of a power transmission system are step-down transformers used?
Answer
(C)
Substations
27
What are the two poles of a magnet?
Answer
(B)
North and South
28
If the input current is 2A and the input voltage is 12V, what is the input power?
Answer
(C)
24 W
29
What is induced in the coil when a magnet is pushed into a coil?
Answer
(A)
An e.m.f.
30
What is the turns ratio of a transformer if the primary coil has 100 turns and the secondary coil has 200 turns?
Answer
(B)
1:2
31
What happens to the magnetic field around a wire when the current flowing through the wire is increased?
Answer
(C)
The magnetic field becomes stronger.
32
How does a hard disk drive store information?
Answer
(C)
By using electromagnets to change the direction of the magnetic field.
33
What is the function of a circuit breaker in a circuit?
Answer
(B)
To open the circuit if the current is too high.
34
In a moving coil loudspeaker, which part vibrates to produce sound?
Answer
(C)
The cone.
35
What is the purpose of an alternator in a car?
Answer
(B)
To charge the battery and power electrical systems.
36
Which of the following is not a main component of a transformer?
Answer
(D)
Resistor
37
What happens to the magnetic field around a wire when the current is decreased?
Answer
(B)
The field strength decreases.
38
What is the unit of measurement for electric current?
Answer
(B)
Ampere
39
If the primary voltage is 240V and the secondary voltage is 12V in a transformer, is it a step-up or step-down transformer?
Answer
(B)
Step-down
40
If you want to increase the output voltage of a generator, what is one thing you could do?
Answer
A
B
41
What type of core material is used in transformers to minimize energy loss due to hysteresis?
Answer
(C)
Soft iron
42
Which component in a D.C. generator performs the same function as slip rings in an A.C. generator?
Answer
(B)
The commutator
43
Which direction does the force of the magnetic force act in a wire?
Answer
(B)
Perpendicular to the magnetic field and current.
44
How is the Earth's magnetic field generated?
Answer
(A)
By the movement of charged particles in the Earth's core.
45
What happens if two unlike poles of two magnets are placed close to each other?
Answer
(A)
They will attract each other.
46
In an electric motor, what creates the magnetic field that interacts with the coil?
Answer
(B)
A separate permanent magnet or electromagnet
47
In a simple electric motor, what is used to reverse the direction of the current flow in the coil?
Answer
(C)
Commutator
48
Which is needed for recording in the magnetic tape?
Answer
(D)
Varying magnetic field
49
What is a magnetic domain?
Answer
(B)
A region where the atoms in a material are aligned.
50
What is the key to the operation of a circuit breaker?
Answer
(A)
An electromagnet.