P3.3 Keeping things moving

Question 1

What is a magnetic field?

Answer 1

A region where magnetic materials (like iron and steal) and also wires carrying currents experience a force acting on them

Question 2

What way do the arrows on field diagrams always point?

Answer 2

From north to south

Question 3

What is an electromagnet?

Answer 3

A magnet whose magnetic field can be turned on or off with an electric current

Question 4

How can you increase the strength of the magnetic field around a coil of wire?

Answer 4

By adding magnetically soft iron core through the middle of the coil.

Question 5

What happens when a current stops through an electromagnet?

Answer 5

it stops being magnetic

Question 6

What are some uses of electromagnets?

Answer 6

-In some cranes- to attracts and pick up things made from magnetic materials.

Question 7

What is the motor effect?

Answer 7

The force experienced by a current carrying wire in a magnetic field

Question 8

How can you increase the force in the motor effect?

Answer 8

• Increase the current
• Increase the magnetic field
• Make sure the wire is at 90 degrees to the magnetic field

Question 9

How do you experience the full force in the motor effect?

Answer 9

Make sure the wire is at 90 degrees to the magnetic field

Question 10

What happens if the direction of the current or magnetic field in the motor effect is reversed?

Answer 10

The direction of the force is reversed too

Question 11

What happens if the wire runs along parallel to the magnetic field in the motor effect?

Answer 11

There will be no force

Question 12

What do each of the 3 fingers stand for in Fleming’s Left Hand Rule?

Answer 12

Thumb= motion

First Finger= field

Second finger= current

Question 13

What do electric motors use to work?

Answer 13

the motor effect

Question 14

What 2 factors speed up an electric motor?

Answer 14

• more current

- stronger magnetic field

Question 15

What does the split-ring commutator do in an electric motor?

Answer 15

reverses the current after every half turn, which keeps the motor rotating in the same direction

Question 16

What is electromagnetic induction?

Answer 16

The creation of a potential difference (voltage) across a conductor which is experiencing a change in magnetic field.

Question 17

Describe how we can make electricity by electromagnetic induction

Answer 17

moving a magnet in coil of wire

OR

moving a coil of wire in a magnetic field

Question 18

In electromagnetic induction, what happens if you move the magnet through a coil of wire in the opposite direction or reverse the polarity of the magnet?

Answer 18

The potential difference/current will be reversed too

Question 19

In electromagnetic induction, what happens if you keep the magnet moving forwards and backwards?

Answer 19

You produce a potential difference that keeps swapping direction

-will produce an ALTERNATING CURRENT

Question 20

How do generators in a power station produce electricity?

Answer 20

By electromagnetic induction.

Keep magnets moving backwards and forwards through a coil

Question 21

What happens when a current flows through a wire?

Answer 21

A magnetic field is produced around the wire

Question 22

Describe the basic structure of a transformer

Answer 22

A primary and secondary coil, joined with an iron core

Coils-copper, electric conductor and covered in plastic

The primary coil is connected to an alternating current

Question 23

Describe how a transformer works?

Answer 23

An alternating current in the primary coil produces a changing magnetic field in the iron core and hence in the secondary coil.

This induces an alternating potential difference across the ends of the secondary coil

Question 24

How can you tell if a transformer is a step up transformer?

Answer 24

They have more turns on the secondary coil than the primary coil

Question 25

How can you tell if a transformer is a step down transformer?

Answer 25

They have more turns on the primary coil than the secondary coil.

Question 26

Describe the potential difference in step up transformer

Answer 26

pd across the secondary coil is greater than the pd across he primary coil

Question 27

Describe the potential difference in step down transformer

Answer 27

pd across the secondary coil is less than the pd across the primary coil

Question 28

What are switch mode transformers?

Answer 28

A type of transformer that operate at higher frequencies than traditional transformers.

Question 29

Between what frequencies do switch mode transformers operate at?

Answer 29

Between 50kHz and 200kHz

Question 30

What are some benefits of switch mode transformers?

Answer 30

much lighter and smaller than traditional transformers working from a 50Hz mains supply. Use little power when they are switched on but not connected to a charging device (when no load is applied)

Question 31

Give an example of what a switch mode transformer is used for

Answer 31

mobile phone chargers

Question 32

In the equation Vp (divided by) Vs = np (divided by) ns what does each letter stand for and what are the units?

Answer 32

Vp- potential difference across the primary coil (V) Vs- potential difference across the secondary coil (V) np- the number of turns on primary coil ns- the number of turns on secondary coil

Question 33

In the equation Vp x Ip = Vs x Is what does each letter stand for and what are the units?

Answer 33

Vp- potential difference in primary coil (V) Ip- current in primary coil (A) Vs- potential difference across secondary coil (V) Is- current in secondary coil (A)

Question 34

When is a magnetic field produced around a wire?

Answer 34

when a current flows through the wire

Question 35

A conductor will not experience a force if it is ........ to the magnetic field

Answer 35

parallel

Question 36

When is the direction of the force reversed?

Answer 36

if either the direction of the current or the direction of the magnetic field is reversed

Question 37

Explain how the motor effect is used to make the drum in a washing machine spin

Answer 37

A motor spins round because it has a coil between magnets. There is a force when a current flows in the circuit and this makes the coil spin faster due to the motor effect