P7

Question 1

What happens when a wire is carrying electric current

Answer 1

a magnetic field is produced around itself

Question 2

Relationship between current and magnetic field (2)

Answer 2

higher the current = greater the magnetic field

reversing current = reversing direction of magnetic field (N and S poles will change ends)

Question 3

Define electric current in wires (2)

Answer 3

flow of electrons around circuit

from positive to negative terminal of battery

Question 4

Dot in centre of wire of diagram

Answer 4

current is directed towards you

Question 5

Cross in centre of wire of magnetic diagram

Answer 5

current is directed away from you

Question 6

Field lines in magnetic diagram

Answer 6

form continuous rings around wire

Question 7

Direction of magnetic field line if current is travelling towards you

Answer 7

anti-clockwise

Question 8

Direction of magnetic field line if current is travelling away you

Answer 8

clockwise

Question 9

Motor Effect (3)

Answer 9

wire will experience force at right angles both to wire + magnetic field

when a wire carrying an electric current passes through a magnetic field at a right angle to wire

size of force depends on magnitude of current + strength of magnetic field

Question 10

Fleming’s left hand rule (3)

Answer 10

thumb = movement

index finger = magnetic field

middle finger = current

Question 11

What happens when charged particle is stationary in a magnetic field

Answer 11

nothing will happen

Question 12

What happens when you move the wire parallel to the magnetic field

Answer 12

nothing will happen

Question 13

What happens when a charged particle moves through the magnetic field at an angle

Answer 13

will experience a sideways force, trying to push it off its path

Question 14

How electric motor is made

Answer 14

coil of wire between poles of 2 permanent magnets

Question 15

How dc motor works (4)

Answer 15

current passes through coil of wire –> creates magnetic field

magnetic field interacts with magnetic field of permanent magnets

two fields exert forces on sides of coil at right angles to permanent magnetic field

motor coil will rotate - one side of coil will experience a force upward, other side of coil will experience a force downward

Question 16

Function of split-ring commutator (2)

Answer 16

reverses direction of current so forces on coil are reversed

allows motor to continue to spin

Question 17

How will a motor spin faster (3)

Answer 17

increasing current

increasing strength of magnetic field

number of turns of wire in coil

Question 18

How will a motor spin in the opposite direction (2)

Answer 18

change direction of current

reverse magnetic field

Question 19

How is an electromotive force created in a wire in a complete circuit (3)

Answer 19

wire moved through magnetic field or

magnetic field moved passed wire or

magnetic field around wire changes strength

Question 20

What does magnitude of electromotive force depend on (3)

Answer 20

field strength

speed which wire moved

increasing number of turns of wire in coil

Question 21

How is a direct current produced

Answer 21

steady current produced by battery from negative terminal of battery to positive terminal

Question 22

Voltage of direct current

Answer 22

stays constant throughout circuit

Question 23

Current of alternating current

Answer 23

electrons in circuit move back and forward

Question 24

Advantage of a.c over d.c

Answer 24

can transmit electricity at high voltages - reduces amount of energy lost

Question 25

Define dynamo

Answer 25

simple current generator

Question 26

How dynamo works (2)

Answer 26

turning permanent magnet inside coil by 180 degrees = reverses magnetic field

change in magnetic field –> induces alternating current

Question 27

What frequency of current in dynamo dependent on

Answer 27

how fast dynamo is spinning

Question 28

How generators work (5)

Answer 28

use rotating electromagnets

pass the rotating magnetic field through stationary coils

spinning coil of wire in magnetic field produces varying e.m.f

current produced is passed to external circuit by slip rings

output is alternating current

Question 29

What is a transformer made of

Answer 29

2 coils of insulated wire on a piece of iron

Question 30

How transformers work (3)

Answer 30

alternating voltage applied to first coil produces changing magnetic field in core

changing magnetic field induces alternating e.m.f in second coil

strength of magnetic field increased as iron is easily magnetised

Question 31

What happens if there are more turns on secondary coil than primary coil in transformer

Answer 31

voltage of secondary coil > voltage of primary oil

Question 32

Transformer primary coil voltage and number formula

Answer 32

primary coil voltage/secondary coil voltage = number of primary turns/number of secondary turns

Question 33

step-up transformer (2)

Answer 33

when number of secondary coil turns > number of primary coil turns

voltage increases in same proportion

Question 34

step-down transformer (2)

Answer 34

when number of secondary coil turns < number of primary coil turns

produces smaller voltage in secondary coil

Question 35

Purpose of transformers (2)

Answer 35

steps up voltage - steps down current vice versa

reduce heat loss

Question 36

Transformer voltage equation

Answer 36

primary coil voltage x primary coil current = secondary coil voltage x secondary coil current