Paper 2 Magnetism

Question 1

What is a magnetic field

Answer 1

The region around a magnet where it has a magnetic effect

Question 2

What happens when iron filings or plotting compasses are placed near the magnet

Answer 2

They point along curved lines known as lines of flux and they show the direction of the magnetic field at each point

Question 3

What direction do the filings always point in

Answer 3

From north pole to south pole

Question 4

What happens when filings are placed near a current carrying wire

Answer 4

They point in circles around the wire and when the current is reversed they point in the opposite direction

Question 5

What’s a wire in a coil shape know as

Answer 5

A solenoid

Question 6

What is the shape of the field line like around a solenoid

Answer 6

It’s the same as around the bar magnet

Question 7

3 key points about field lines

Answer 7

Never touch or cross
The closer together the lines are the stronger the field
Direction of field line shows direction of force that would act on a tiny N-pole placed at that point

Question 8

What are molecular magnets

Answer 8

They are tiny magnets with N and S poles

Question 9

What does saturated mean

Answer 9

Is when all molecular magnets are aligned

Question 10

Properties of soft magnetic materials

Answer 10

It’s easy to magnetise and will demagnetise quickly, useful in electromagnets which can turn off magnets quickly e.g. iron

Question 11

Properties of hard magnetic materials

Answer 11

Harder to magnetise and harder to demagnetise. perfect for permanent magnets e.g needle in compass e.g steel

Question 12

What’s an electromagnet

Answer 12

A solenoid (coil of wire) with an iron core. It’s a temporary magnet (can be turned on and off)

Question 13

How do electromagnets work

Answer 13

When a current is passed along the wire, a magnetic field is created an the iron core is magnetised
when the current is switched off the iron bar loses its magnetism

Question 14

How can the strength of the magnetic field be increased

Answer 14

Increasing voltage so current increases
Increasing the number of turns in the coil
Inserting an iron core

Question 15

What is 1 tesla equal to

Answer 15

One Newton per amp per metre

Question 16

Force =

Answer 16

Flux density x length of conductor in field x current

Question 17

What does a simple electric motor consist of

Answer 17

A rectangular coil wire, which is placed inside a magnetic field and can rotate between the poles of a magnet, a split ring commutator and a brush contact

Question 18

How does a simple electric motor work

Answer 18

When the coil turns 90* (so the coil is vertical) the current stops flowing because gaps in the commutator break the current but still turns because of its own movement
When brushes make contact again both the commutator and coil have turned over look in book

Question 19

How does Flemming’s left hand rule work

Answer 19

Forefinger- direction of field
Middle finger- current
Thumb- movement

Question 20

What are the two ways of reversing the direction of the forces on the coil in the electric motor

Answer 20

Reverse the direction of the current

Reverse the poles

Question 21

Electromagnetic induction (the generator effect)

Answer 21

When a wire (conductor) cuts through magnetic field lines a voltage is induced across ends of conductor this is electromagnetic induction as the electrons in the wire have been given a push

Question 22

What happens if the wire is stationary (the generator effect)

Answer 22

No field lines are cut so no voltage is induced

Question 23

What happens if the wire moves parallel to the field lines (the generator effect)

Answer 23

No field lines are cut so no voltage is induced

Question 24

What happens if you move the wire faster or use a stronger magnet (the generator effect)

Answer 24

The voltage used inceases

Question 25

What happens if you move the wire in the opposite direction or reverse the magnetic field (the generator effect)

Answer 25

Then the voltage induced will be reversed

Question 26

What’s a bicycle dynamo and how does it work

Answer 26

Consists of a magnet that rotates near a coil of wire (wound on a soft iron core) so that the lines of ‘flux’ cut the wire

Question 27

A generator converts…energy into…energy

Answer 27

Kinetic energy into electrical energy

Question 28

Why can a generator be though of as a ‘motor operating in reverse’

Answer 28

Because a motor converts electrical into kinetic which is opposite to a generator

Question 29

How does a microphone work

Answer 29

The diaphragm of a microphone is attached to the coil. When the diaphragm vibrates in response to incoming sound waves, the coil moves backwards and forwards past the magnet. This induces a current in the coil alternating direction when the diaphragm does

Question 30

How is a transformer constructed

Answer 30

Consists of primary and secondary coil wrapped around the iron core. 2 coils aren’t connected electrically. This is achieved by using an insulated wire so no current flows through the iron between the 2 coils. 2 coils only connected by magnetic field

Question 31

How do transformers work

Answer 31

When current flows in primary coil it becomes an electromagnet so iron core magnetised which is linked to 2dary coil and as A.C is used a voltage is induced in the 2dary coil

Question 32

How do we know an A.C is used in a transformer

Answer 32

The magnetic field in the 2dary coil keeps changing (size and direction) and so a voltage is induced in the 2dary coil. Since the magnetic field changes direction, the voltage induced will also change so must be A.C

Question 33

Voltage across primary (Vp)/voltage across secondary (Vs)=

Answer 33

Number of turns on primary (Np)/Number of turns on secondary (Ns)