Sign In

Physics for IGCSE & O level - Magnets And Currents (Section 10)

1
What is the primary function of a step-down transformer?
Answer
(B)
Decrease the voltage.
2
What type of current does a transformer work with?
Answer
(B)
Alternating Current (AC)
3
In a magnetic field, what direction does a compass needle align itself?
Answer
(A)
Parallel to the field lines.
4
In an ideal transformer, what remains constant (assuming no losses)?
Answer
(C)
Power.
5
What is the effect of moving a magnet near a coil?
Answer
(B)
A current is induced in the coil.
6
What are the two key components used in the basic structure of an electromagnet?
Answer
(B)
Iron core and wire coil
7
The changing magnetic field in a transformer core induces a voltage in the:
Answer
(B)
Secondary coil
8
What is the role of slip rings in an a.c. generator?
Answer
(C)
To connect the coil to the external circuit.
9
Which of the following is the correct relationship between voltage and current in an ideal transformer?
Answer
(B)
Voltage and current are inversely proportional.
10
In what direction does the turning force act on a coil?
Answer
(B)
Perpendicular to the magnetic field and current.
11
What does Fleming's Left-Hand Rule help determine?
Answer
(C)
The direction of force on a current-carrying wire in a magnetic field.
12
What type of materials are attracted to magnets?
Answer
(B)
Magnetic.
13
What does Lenz's law state?
Answer
(B)
The induced current opposes the change that produces it.
14
Which of the following methods can be used to demagnetize a magnet?
Answer
A
B
15
What happens to the direction of the induced current when the motion of the magnet is reversed?
Answer
(A)
The direction of the induced current reverses.
16
What is the rule used to determine the direction of the force on a current-carrying wire in a magnetic field?
Answer
(B)
Fleming's Left-Hand Rule
17
What does the direction of the induced current depend on?
Answer
(C)
The direction of the magnet's movement.
18
What happens to the direction of the induced current if the magnet is pulled out of the coil?
Answer
(A)
The direction of the induced current is reversed.
19
What are the key components of a transformer?
Answer
A
B
C
20
What is the Earth's magnetic field?
Answer
(D)
A magnetic field that acts as if there is a large bar magnet inside the Earth.
21
What is demagnetization?
Answer
(C)
Removing the magnetic properties from a magnet.
22
What is a magnetic field?
Answer
(A)
The area around a magnet where its force is felt
23
What happens when a current flows through a wire?
Answer
(A)
A magnetic field is created around the wire.
24
How is an electromagnet similar to a permanent magnet?
Answer
(A)
It has two poles.
25
What is the effect of placing a piece of iron inside a coil of wire carrying a current?
Answer
(C)
The strength of the magnetic field increases.
26
Which of the following would NOT increase the voltage of a generator?
Answer
(D)
Using direct current.
27
In a transformer, the core material is usually made from
Answer
(C)
Soft Iron
28
What type of energy is stored in a magnetic field?
Answer
(D)
Magnetic Energy
29
How are electromagnets used in hard disk drives?
Answer
(B)
To read and write data on the disk
30
If a transformer's turns ratio is 1:4 and the primary voltage is 120V, what is the secondary voltage?
Answer
(A)
30 V
31
Which of the following is the best method to minimize energy loss in a transformer?
Answer
A
B
32
What will change if the direction of the coil's current is reversed?
Answer
(B)
The direction of the turning effect
33
What is the primary function of a transformer?
Answer
(B)
To change the voltage of alternating current.
34
Which is a factor affecting the output of a generator?
Answer
(D)
All of the above.
35
What is the relationship between the input and output power of an ideal transformer?
Answer
(C)
Input power equals output power.
36
What is the term used for the creation of a temporary magnet by placing a material, such as iron, within a magnetic field?
Answer
(B)
Magnetic induction
37
In a power transmission system, transformers are used to ____ the voltage for transmission.
Answer
(A)
increase
38
Which of the following is a factor affecting the efficiency of a transformer?
Answer
(D)
All of the above
39
How does the magnetic field around a wire change when it carries a larger current?
Answer
(C)
It becomes stronger.
40
What causes a permanent magnet to have a magnetic field?
Answer
(B)
The alignment of the atoms in the material.
41
What is the function of a core in a transformer?
Answer
(B)
To provide a path for the magnetic flux.
42
Which of the following correctly describes the relationship between magnetic fields and current-carrying wires?
Answer
(B)
Magnetic fields are generated by moving charges.
43
The efficiency of a transformer is primarily reduced by:
Answer
(C)
The resistance in the core and the coils
44
How can a magnet be used to produce electricity?
Answer
(B)
By moving the magnet relative to a coil of wire.
45
What happens to the magnetic field around a current-carrying wire if the direction of the current is reversed?
Answer
(C)
The magnetic field reverses direction.
46
What is the role of the brushes in an electric motor?
Answer
(B)
To provide current to the rotating coil.
47
What is the main difference between an A.C. and a D.C. generator?
Answer
(B)
A.C. generator uses slip rings, D.C. uses a commutator.
48
When power is transmitted over long distances, a major loss can occur due to
Answer
(A)
Resistance in cables
49
How can you increase the force experienced by a current-carrying wire in a magnetic field?
Answer
A
B
C
50
What is the primary component used in a loudspeaker that utilizes electromagnetism?
Answer
(B)
A permanent magnet and a coil of wire