Section 6

Question 1

magnetic field definition

Answer 1

a region where magnetic materials experience a force

Question 2

how to look at magnetic field patterns

Answer 2

• compasses

- use multiple compasses to see the magnetic field lines coming out of a bar magnet or two bar magnets

Question 3

‘soft’ magnet definition

Answer 3

loses its induced magnetism easily

Question 4

how does a wire move in a magnetic field?

Answer 4

the wto magnetic fields of the two poles affect one another which results in a force on the wire

Question 5

field

Answer 5

first finger

Question 6

current

Answer 6

second finger

Question 7

motion

Answer 7

thumb

Question 8

four factors which speed up electric motors

Answer 8

• more current
• more turns
• stronger magnetic field
• soft iron core in the middle

Question 9

how to reverse the direction of a motor

Answer 9

• swap the polarity of the d.c supply

- swap the magnetic poles over

Question 10

what is s split ring communicator?

Answer 10

-swaps the contacts every half turn to keep the motor rotating in the same direction

Question 11

how do loud-speakers work?

Answer 11

• a.c electrical signals from an amplifier are fed to a coil of wire in the speaker
• the coil is surrounded by a permanent magnet, so the a.c signals cause a force on the wire
• the wire moves back and forth
• the speaker vibrates

Question 12

electromagnetic induction

Answer 12

the operation of a voltage in a wire which is experiencing a change in magnetic field

Question 13

two situations where you find electromagnetic induction

Answer 13

• an electrical conductor moves through a magnetic field

- the magnetic field through an electrical conductor changes

Question 14

how to get a bigger voltage through em induction

Answer 14

• increase the strength of the magnet
• increase the number to turns on the coil
• increase the speed of movement

Question 15

a.c generators- how do they work?

Answer 15

• spin coil
• current is induced in the coil
• current changes direction every half turn

Question 16

slip rings and brushes

Answer 16

make sure that the contacts don’t swap every half-turn

Question 17

how do transformers work?

Answer 17

• a.c voltage is applied
• iron core magnetises and de magnetises quickly
• a.c voltage induced in secondary coil

Question 18

relationship between primary and secondary voltages

Answer 18

-the ratio between the two voltages is the same as the number of turns on the two coils