Magnetism

Question 1

List magnetic materials

Answer 1

Iron
Steel
Nickel
Cobalt

Question 2

What are ferromagnetic materials?

Answer 2

Iron

Steel

Question 3

Give an example of a hard magnet material

Answer 3

Steel

Question 4

What does a hard magnetic material mean?

Answer 4

Hard to magnetize- long time to magnetize

Permanent magnet

Question 5

What does a soft magnetic material mean?

Answer 5

Easy to magnetise- short time to magnetize

Temporary magnet

Question 6

Why are some materials attracted to magnets?

Answer 6

Because of the existence of tiny magnets inside. When a magnetic is brought near it, its tiny magnets are arranged uniformly

Question 7

How can magnetism be made?

Answer 7

By induction
By stroking
By electrically

Question 8

How can you magnetise electrically?

Answer 8

Place magnetic material in a solenoid connected to dc current

Question 9

How can magnetism be destroyed?

Answer 9

Hammering a magnet
Heating
Dropping a magnet
Demagnetising by using reduced AC through a coil of wire wrapped round a magnet

Question 10

What is the magnetic field?

Answer 10

The area around a permanent magnet or a wire carrying a current.

Question 11

Describe the straight wire’s magnetic field

Answer 11

Concentric circles

Question 12

What can a solenoid be used for?

Answer 12

Circuit breaker

Magnetic relay

Question 13

What is the purpose of a relay?

Answer 13

Control high voltage system with low voltage or control high current system with low current

Question 14

Describe the relay process

Answer 14

The low voltage circuit is on so there is a current in the solenoid. The magnetic field in the solenoid attracts the armature and the current flows through the contacts so the high voltage is on.

Question 15

What is a circuit breaker?

Answer 15

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.

Question 16

What increases the magnetic force?

Answer 16

Increasing current
Stronger magnet
Increasing length of wire in the field

Question 17

What are parts of an electrical motor

Answer 17

Coil of wire
Two magnets
Split ring commutator
Brushes

Question 18

How does the electrical motor work?

Answer 18

1. The current flows in opposite directions on each side of the armature which will create two opposite forces act as different line making the armature only spin half a cycle
2. The split-ring reverses the current direction through an armature every half turn so the armature will continue to spin in the same direction

Question 19

What increases the turning effect?

Answer 19

Increasing current
Increasing number of turns
Increasing area of the coil
Using a stronger magnet

Question 20

What happens when the coil is horizontal?

Answer 20

The turning effect will be maximum

Question 21

What happens as the turning effect as the coil rotates from horizontal to vertical?

Answer 21

It decreases

Question 22

What is faraday’s law?

Answer 22

The EMF induced in a conductor is proportional to the rate at which magnetic field lines are cut by the conductor

Question 23

What increases the induced EMF?

Answer 23

Moving wire faster
Stronger magnet
Increasing the length of wire inside the magnetic field

Question 24

What is a galvanometer?

Answer 24

A very sensitive ammeter

Question 25

What is Lenz's Law?

Answer 25

An induced current always flows in the direction such opposes the change which produced it

Question 26

How can the size of the current be made bigger?

Answer 26

Magnet at a faster speed Stronger magnet More turns of wire on the coil

Question 27

What does an AC generator convert?

Answer 27

Mechanical work into electrical work

Question 28

How does an AC generator work?

Answer 28

1. The wire cuts the m.f lines inducing an emf that causes induced current in the coils. 2. If the wire is moved in the opposite direction the induced current also moves in the opposite direction This means that as a coil is rotated in magnetic field, the induced current reverses direction every half turn. This is called alternating current.

Question 29

How do I increase EMF in the AC generator?

Answer 29

Increase number of turns Use a stronger magnet Increase the area of the coil Rotating the coil faster

Question 30

What are the types of transformers?

Answer 30

Step up transformer | Step down transformer

Question 31

What is a transformer made from?

Answer 31

Two coil and one on each side of a soft iron core

Question 32

Explain how the transformer can work

Answer 32

AC current passes through the primary core which creates a changing magnetic field in the iron core. The changing magnetic field then induces alternating current in the secondary coil. The induced emf depends on the number of coils in the secondary coils.

Question 33

Transformer equation

Answer 33

Voltage A/ Voltage B= Number of turns in A/ Number of turns in B

Question 34

Why do transformers only work with alternating current?

Answer 34

Using direct current will create a mf in the core but it will not be a changing mf and so no voltage will be induced in the second coil

Question 35

Power in the transformer

Answer 35

V1 * I1= V2 * I2

Question 36

Why does a transformer produce a very high voltage?

Answer 36

Minimise energy loss as current decreases therefore it is less expensive