P4

Question 1

what is a magnetic field

Answer 1

a region where a magnetic material experiences a force

Question 2

what are magnetic field lines used to show

Answer 2

size and direction of magnetic fields

Question 3

what way do magnetic field point

Answer 3

north TO south

Question 4

what is the strength of the magnetic field called

Answer 4

magnetic flux density

Question 5

like poles what

Answer 5

repel

Question 6

opposite poles what

Answer 6

attract

Question 7

when a magnet is brought near a magnetic material then the material acts as what

Answer 7

a magnet

Question 8

what is it called when the material acts a magnet

Answer 8

an induced magnet

Question 9

an electric current in a material produces a what

Answer 9

a magnetic field

Question 10

how do you find direction if the field around a straight wire

Answer 10

right hand rule

Question 11

what happens to the magnetic field if its further from the wire

Answer 11

magnetic field gets weaker

Question 12

what happens to the magnetic field around a flat circular coil

Answer 12

there are ellipses - stretched of magnetic field lines around the coil

Question 13

what is a solenoid

Answer 13

lots of coils of wire joined together

Question 14

what is the field like on the outside of the solenoid

Answer 14

same as a bar magnet

Question 15

how to increase the magnetic effect at the ends of a solenoid

Answer 15

• current in wire is increased
• number of turns of coil
  increase
• length of solenoid decreases
• iron core is added inside solenoid

Question 16

what happens when a wire is out between magnetic poles

Answer 16

a force on the wire occurs

Question 17

what degree does the wire have to be at to experience full force

Answer 17

90 degrees

Question 18

how can the force get stronger

Answer 18

if either the current or magnetic field is made stronger

Question 19

how do you find direction of the force on a current - carrying conductor

Answer 19

flemings left hand rule

Question 20

what does the thumb stand for in left hand rule

Answer 20

force

Question 21

what does the first finger stand for in left hand rule

Answer 21

field

Question 22

what does the second finger stand for in left hand rule

Answer 22

current

Question 23

where does a coil sit in a motor

Answer 23

between the opposite poles of a magnet

Question 24

how does current flow on each side of the coil (motor)

Answer 24

in opposite directions

Question 25

each side of the coil is _____ to the magnetic field (motor)

Answer 25

perpendicular

Question 26

why does the coil rotate (motor)

Answer 26

it is on a spindle and the forces act in opposite directions on each side - spins

Question 27

what does a split ring commutator do in a motor

Answer 27

swapping contact every half turn so it rotates in the same direction

Question 28

how can direction of motor be changed

Answer 28

reversing current or swapping magnetic poles over

Question 29

how to speed up motor

Answer 29

- increase the current - add more turns to coils - increase magnetic flux density

Question 30

what else can the force between a current - carrying coil of wire and a magnet do

Answer 30

moves things back and forth e.g loudspeaker

Question 31

what does a loudspeaker contain

Answer 31

a coil of wire surrounded by a magnet and another magnet inside the coil

Question 32

what type of electrical signals are fed to the coil of the wire (loudspeaker)

Answer 32

a.c - alternating current

Question 33

the interaction between the magnetic field and the current in the coil forces the coil do to what (loudspeaker)

Answer 33

move in one direction

Question 34

because the its an a.c in the loudspeaker the current then does what

Answer 34

changes direction - coil moves back in the other direction

Question 35

as the current continues continues to alternate the coil does what (loudspeaker)

Answer 35

moves back and forth

Question 36

these movements make what vibrate (loudspeaker)

Answer 36

the cone

Question 37

what does this create in the air (loudspeaker)

Answer 37

pressure variations - e.g sound

Question 38

what does a changing magnetic field induce in a conductor

Answer 38

a potential difference

Question 39

what is an electromagnetic induction

Answer 39

when a potential difference is induced across a conductor which is experiencing a change in its external magnetic field

Question 40

what happens if direction of rotation is reversed

Answer 40

direction of induced p.d / current reverses

Question 41

what do some alternators do

Answer 41

rotate a magnet in a coil of wire

Question 42

what happens as this magnet spins (alternator)

Answer 42

an alternating p.d is induced across the ends of coil

Question 43

what happens to p.d every half turn (alternator)

Answer 43

changes direction because direction of field changes as magnet rotates

Question 44

what type of current do alternators generate

Answer 44

a.c (alternating current)

Question 45

what do the slip rings at the ends of the coils do (alternator)

Answer 45

remain in contact with brushes that are connected to rest of circuit so so contact don't swap every half turn

Question 46

what type of current do dynamos generate

Answer 46

d.c (direct current)

Question 47

what does the output p.d and current do every half rotation of the coil to produce d.c (dynamo)

Answer 47

changes direction

Question 48

what swaps the connection every half turn to keep current flowing in the same direction (dynamo)

Answer 48

split ring commutator

Question 49

what is different about a microphone and a loudspeaker

Answer 49

cone (loudspeaker) is replaced by diaphragm (microphone)

Question 50

what causes the diaphragm to move back and forth when hit by them (microphone)

Answer 50

sound waves (pressure variations)

Question 51

the diaphragm moving means the wire moves and does what (microphone)

Answer 51

induces a p.d across ends of the of the coil of the wire

Question 52

what does the induced p.d mean (microphone)

Answer 52

variations in current in the electrical current

Question 53

what do transformers do

Answer 53

change the potential difference of a.c

Question 54

how many coils to transformers have

Answer 54

2 coils

Question 55

what are the 2 coils joined by (transformers)

Answer 55

an iron core

Question 56

what is produced when an alternating p.d is applied across the primary coil (transformers)

Answer 56

an alternating magnetic current

Question 57

why does the iron core become magnetised (transformers)

Answer 57

iron is a magnetic material

Question 58

the coil producing a alternating magnetic field does what (transformers)

Answer 58

alternates magnetisation in the core

Question 59

what does a changing magnetic field induce (transformers)

Answer 59

a p.d in the secondary coil

Question 60

what do step down transformers do

Answer 60

step voltage down - more turns on primary coil

Question 61

what do step up transformers do

Answer 61

step voltage up - more turns on secondary coil