P4

Question 1

north pole field lines

Answer 1

go outwards

Question 2

south pole field lines

Answer 2

go inwards

Question 3

how to see magnetic field patterns

Answer 3

Put magnet under a piece of paper + scatter iron fillings on top, they will align themselves w the field lines

Question 4

how to see magnetic field patterns with a compass

Answer 4

1. Put magnet on paper
2. place compass on the paper next to the mag
3. mark dots where the needle is pointing to
4. move compass to point and repeat at diff points
5. join them up

Question 5

Permanent magnet

Answer 5

All domains (small magnetic regions) line up always

Question 6

Induced magnet

Answer 6

When in a magnetic field, regions that aren’t lined up, line up and become magnetic

Question 7

how does a magnetic compass prove the Earth’s core must be magnetic

Answer 7

Compasses always point north when they aren’t near a magnet - evidence that earth has a magnetic north/south pole

Question 8

Symbol for current going towards you + direction of field lines

Answer 8

dot, acw

Question 9

Symbol for current going away from you + direction of field lines

Answer 9

cross, cw

Question 10

rule to find out direction of magnetic field around a current

Answer 10

Right hand rule

Question 11

fleming’s left hand rule

Answer 11

thumb - force
First Finger - Field
seCond finger - Current

Question 12

Motor components

Answer 12

• current carrying coil between 2 opposite poles
• split ring commutator
• coil spins

Question 13

split ring commutator

Answer 13

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

Question 14

how to reverse the direction of the motor

Answer 14

reverse current/reverse fields

Question 15

Electromagnetic Induction components (generator principle)

Answer 15

• Induced p.d. produced if wire is in a changing magnetic field
• field lines need to be CUT to induce p.d.
• move magnet in and out of coil of wire/ or move wire in magnet

Question 16

How to increase induced p.d.

Answer 16

• more wire (induce p.d. in each loop so total p.d. increases)
• move wire faster
• stronger magnetic field (as you will be cutting more field lines p second)

Question 17

alternator

Answer 17

type of generator that produces ALTERNATING p.d.

Question 18

how does an alternator work

Answer 18

• Coil of wire spins between poles of a magnet

- slip rings used to produce perfect a.c.

Question 19

Dynamo

Answer 19

type of generator that produces a DIRECT CURRENT

Question 20

how does a dynamo work

Answer 20

Same arrangement as a motor - SPLIT ring commutator used

Question 21

Basics of transformers

Answer 21

• Alternating p.d supplied = a.c. in p coil = field lines around coil continually change
• this produces a changing magnetic field in the iron core
• which in turn induces a changing p.d. in the secondary coild

Question 22

In a transformer power always…

Answer 22

is equal

primary p.d x current = secondary p.d. x current

Question 23

how does a dynamic microphone work

Answer 23

(use electromagnetic induction) ,

• sound wave is a pressure wave, as it hits the diaphragm, areas of compressions (high p) push it in and areas of low pressure (rarefaction) pull it ou
• as diaphragm moves in + out so does coil(has magnet in the centre)
• p.d. induced at the ends = electrical signal produced by a microphone

Question 24

How does a loudspeaker work

Answer 24

(like a motor)

• changing p.d = changing current
• The coil is inside a permanent magnets magnetic field so it experiences a changing magnetic force
• diaphragm attached to coil therefore moves in + out = produces a sound wave of the same freq the diaphragm vibrates

Question 25

Why are isolating transformers used?

Answer 25

To prevent direct contact w live wire and socket = reduces risk of electrocution