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Physics for IGCSE & O level - Magnets And Currents (Section 2)

1
What is the direction of a magnetic field?
Answer
(A)
From the north pole to the south pole
2
In a well-designed transformer, what is the relationship between input and output power (neglecting losses)?
Answer
(C)
Input power equals output power.
3
What is used for the mains?
Answer
(A)
Alternating current (a.c.)
4
Which statement best describes a motor?
Answer
(A)
A device that converts electrical energy to mechanical energy.
5
Which materials are most strongly attracted to a magnet?
Answer
(A)
Ferromagnetic
6
What is the function of the core in a transformer?
Answer
(B)
To provide a path for the magnetic field
7
What is the role of a magnetic relay in a circuit?
Answer
(B)
To allow a small current to control a larger one.
8
How can the direction of the force on a wire be predicted?
Answer
(C)
Using Fleming's left-hand rule.
9
What is the purpose of the brushes in a DC motor?
Answer
(A)
To make contact with the rotating commutator.
10
What happens when a current-carrying wire is placed in a magnetic field?
Answer
(B)
A force is exerted on the wire
11
What is the key difference between slip rings and a commutator?
Answer
(A)
Slip rings are for AC, and commutators are for DC.
12
What are the main components in a practical transformer?
Answer
(A)
Core and coils
13
Which of the following are factors that influence the strength of the magnetic field of an electromagnet?
Answer
A
B
C
14
What component in a DC motor is used to reverse the current's direction and keep the motor spinning?
Answer
(B)
Commutator
15
What are the main objectives of a cross-country power transmission system?
Answer
B
C
D
16
Which is the best description of induced magnetism?
Answer
(C)
Magnetism created by the presence of another magnet.
17
If a transformer doubles the voltage, what happens to the current (assuming no energy loss)?
Answer
(B)
Halves
18
What are the two main ways of arranging the coils and the core in a practical transformer?
Answer
A
D
19
What happens when unlike poles of two magnets are brought close together?
Answer
(B)
They attract.
20
What happens when a magnet is heated to a high temperature?
Answer
(B)
It demagnetizes.
21
What is an electric field?
Answer
(B)
The region around a charged object where electric force is exerted
22
In the context of electromagnetic induction, what does the rate of change of magnetic flux link to?
Answer
(B)
The induced e.m.f.
23
What type of device uses an electromagnet to open and close a circuit?
Answer
(B)
A circuit breaker.
24
In a transformer, when the output voltage is greater than the input voltage, it is a:
Answer
(A)
Step-up transformer
25
What type of current does a transformer work with?
Answer
(A)
AC only
26
What is the function of a rectifier in a circuit?
Answer
(A)
To convert AC to DC.
27
What type of core increases the strength of an electromagnet?
Answer
(C)
Iron core.
28
What is the purpose of the split ring commutator in a DC motor?
Answer
(B)
To reverse the current direction in the coil.
29
What kind of current is necessary for transformers to work?
Answer
(B)
Alternating Current (AC)
30
If the current in a coil is reversed, what happens?
Answer
(B)
The direction of the magnetic field reverses.
31
What is the purpose of laminated sheets in a transformer core?
Answer
(B)
To reduce heating effects.
32
What type of current is produced by a simple AC generator?
Answer
(B)
Alternating current (AC)
33
What is the difference between hard and soft magnetic materials?
Answer
(D)
Hard materials retain magnetism.
34
Which method can be used to create a magnet?
Answer
(B)
Stroking it with a magnet.
35
How does the current in the primary coil relate to the current in the secondary coil of a transformer?
Answer
(B)
The ratio of the currents is inversely proportional to the turns ratio.
36
Where does the magnetic field come from?
Answer
(A)
Electric charges in motion
37
How does increasing the current affect the magnetic field strength?
Answer
(C)
It increases the field strength.
38
How can a piece of steel be turned into a permanent magnet?
Answer
(B)
Stroking it with another magnet.
39
What does a transformer with a turns ratio of 1:1 do to voltage and current?
Answer
(C)
Changes neither.
40
What is the unit for measuring power?
Answer
(C)
Watt
41
What does a magnetic relay allow?
Answer
(A)
A small current to control a larger current.
42
In an induction hob, where is the heat produced?
Answer
(B)
In the cookware (pan).
43
What happens to the current in the secondary coil if the number of turns is increased in the secondary coil of a transformer?
Answer
(B)
Decreases
44
In the context of generators, what is the main function of a magnetic field?
Answer
(B)
To facilitate the production of a voltage.
45
Which term describes a material that is attracted to magnets?
Answer
(A)
Ferromagnetic
46
What does a rectifier do?
Answer
(A)
Changes AC to DC
47
What is the relationship between the input and output power of an ideal transformer?
Answer
(C)
Output power equals input power (ignoring losses).
48
What is Lenz's law?
Answer
(A)
The induced current opposes the change causing it.
49
In a transformer, the power output is ideally equal to:
Answer
(B)
The input power.
50
What is the purpose of a circuit breaker in a circuit?
Answer
(C)
To prevent too much current.