Physics - magnetism and electromagnetism

Question 1

Magnetic field

Answer 1

A region where other magnets or magnetic materials experience a force

Question 2

What are the 4 magnetic materials

Answer 2

Iron
Cobalt
Steel
Nickel

Question 3

In a magnetic field drawing in what direction do the lines go in

Answer 3

From north to south

Question 4

In a magnetic drawing the closer together the lines are …

Answer 4

The stromger the magnetic field

Question 5

The force between a magnet and a magnetic material is __________

Answer 5

Always attractive no matter the pole

Question 6

How do compasses work

Answer 6

In a compass there is a tiny bar magnet. The north pole of this magnet is attracted to the south pole of any other magnet it is near, so the compass points in the direction of the magnetic field it is in.

Question 7

When their not near a magnet where do compasses always point

Answer 7

North as the Earth generates its own magnetic field, which shows the inside (core) of the Earth must be magnetic.

Question 8

What are the two types of magnets

Answer 8

Permanent and induced

Question 9

Permanent magnets

Answer 9

Produce their own magnetic field

Question 10

Induced magnets

Answer 10

Magnetic materials that turn into a magnet when they’re put into a magnetic field

Question 11

The force between permanent and induced magnets is __________

Answer 11

always attractive

Question 12

What happens when a current flows through a wire

Answer 12

A magnetic field is created around the wire

Question 13

What is the magnetic field made up of

Answer 13

Made up of concentric circles perpendicular to the wire, with the wire in the centre

Question 14

If you change the direction of the current how does this affect the direction of the magnetic field

Answer 14

Changes direction of the magnetic field

Question 15

What is solenoid

Answer 15

Coil of wire with a permanent magnet inside of it

Question 16

How can you increase the strength of the magnetic field using a solenoid

Answer 16

• More turns in the coil
• Increase strength of magnet
• Increase current

Question 17

Describe the magnetic field inside the solenoid

Answer 17

Strong and uniform - has the same strength and direction at every point in that region

Question 18

Whats the point of putting an iron block in the centre of the coil

Answer 18

Increases the field strength of the solenoid as this iron core becomes an induced magnet whenever current is flowing.

Question 19

What is a solenoid with an iron core called

Answer 19

An electromagnet

Question 20

Why electromagnets useful

Answer 20

Because they’re so quick to turn on and off or because they can create a varying force

Question 21

Uses of electromagnets

Answer 21

• used in cranes to attract and pick up things
• used with other circuits to act as switches

Question 22

When can cause the motor effect

Answer 22

When you put a current-carrying wire in a magnetic field

Question 23

How does the motor effect work

Answer 23

When a current-carrying wire is put between magnetic poles the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and conductor to exert a force on each other causing the wire to move.

Question 24

To experience full force where does the wire have to be

Answer 24

Exactly 90 degrees to the magnetic field

Question 25

The magnitude (strength) of a force increases with

Answer 25

The strength of the magnetic field
Amount of current passing throughout the conductor

Question 26

What are the three things that a force acting on a conductor in a magnetic field depends on

Answer 26

• The magnetic flux density (strength of the magnetic field)
• The size of the current
• The length of the conductor thats in the magnetic field

Question 27

What happens in a basic DC motor

Answer 27

Forces act on the two sides arms of a coil of wire that’s carrying a current.

Question 28

Why does one force act up and one force act down (rotate) in electric motors and loudspeakers

Answer 28

Because the coil is on a spindle

Question 29

What does the split ring communicator do

Answer 29

Swaps the contacts every half turn to keep the motor turning in the same direction

Question 30

How can the direction of the motor be reversed

Answer 30

• By swapping the polarity of the dc supply
• swapping the magnetic poles over

Question 31

How do electric motors and loudspeakers

Answer 31

A cone with a coil of wire wrapped around one end is connected to an alternating current electric supply. The permanent magnet goes inside the coil of wire. As the. current passes through the coil it generates a magnetic field. The magnetic field from the coil now interacts with the magnetic field from the magnet which produces a resultant force causing the cone to move. This causes the cone to move in and out generating sound waves.

Question 32

How do we change the frequency that a cone vibrates in a speaker

Answer 32

By changing the frequency of the ac supply

Question 33

What happens if we increase the size of the current

Answer 33

We increase the amplitude of the vibration thus the volume.

Question 34

What happens if we move a wire up through a magnetic field

Answer 34

A voltage is induced across the end on the wire

Question 35

Induced potential

Answer 35

When a pd reverses

Question 36

Generator effect

Answer 36

The induction of a potential differences in a wire which is moving relative o a magnetic field or experiencing a change in magnetic field

Question 37

When do we get an induced current or induced potential

Answer 37

When we you move a wire through a magnetic field or if we keep the wire still and move the magnetic field.

Or

Putting a magnet through a coil of wire

Question 38

When do we only see the generator effect

Answer 38

When the wire passes through a magnetic field

Question 39

The induced potential difference is larger when

Answer 39

We use a stronger magnetic field
If we move the wire more rapidly
If we shape the wire into a coil (the more turns in a coil the better)

Question 40

Why is it hard for the magnet in a coil to push in and out

Answer 40

The induced current creates its own magnetic field which opposes the movement of a magnet. Eg. when we insert the north pole into the coil that end of the current also becomes a north pole repelling the magnet and making it harder to push in. When we pull the magnet out, that end of the coil becomes the south pole which attracts the magnet making it hard to pull out.

Question 41

Because the induced current makes it harder to move the magnet ….

Answer 41

We are doing work. We are transferring energy from the movement of the magnet into the movement of the current.

Question 42

An alternator

Answer 42

A device that makes use of the generator effect to generate alternating currents

Question 43

What do commutators do

Answer 43

Allow the current to pass out of the coil

Question 44

When is a pd induced in alternators

Answer 44

When a wire passes through the magnetic field

Question 45

Hows does an alternator produce an alternating pd

Answer 45

Because the two sides of the coil are attached to two different rings an alternator produces an alternating pd and current.

Question 46

How do we increase the size of the ac

Answer 46

Increase the strength of the magnetic field
Increase the number of turns on coil or area
Increase rotation speed of coil

Question 47

Dynamo current

Answer 47

Produces a direct current. PD and current do not reverse when the current rotates

Question 48

Split ring commutator

Answer 48

Has two sides separated by a gap each side of coil is connected to one side of the commutator

Question 49

What does the split ring commutator ensure the coil rotates in one direction

Answer 49

The split-ring commutator swaps the positive and negative connections every half turn.
Therefore, the direction of the current through the coil reverses every half turn.
This means that the forces acting on the coil will always be acting in the same direction.
This causes the coil to rotate continuously in one direction.