P15

Question 1

Magnet rules

Answer 1

like poles repel and unlike poles attract

Question 2

magnet field lines

Answer 2

the magnetic field lines of a bar magnet curve around from the north pole of the magnet to the south pole

Question 3

distance from magnet

Answer 3

the greater the distance from the magnet, the weaker the strength of the magnetic field

Question 4

induced magnetism

Answer 4

magnetism created in an unmagnetized magnetic material when the material us placed in the magnetic field

Question 5

permanent magnets

Answer 5

steel is used instead of iron to make permanent magnets, because steel does not lose its magnetism easily, but iron does

Question 6

field lines around a wire

Answer 6

magnetic field lines around a wire are circles centred on the wire in a plane perpendicular to the wire

Question 7

solenoids

Answer 7

• long coil of insulated wire
• used in devices where strong magnetic field needs to be produced
• magnetic field increases strength when current increases
• reverses direction of currents reversed

Question 8

inside the solenoid

Answer 8

magnetic field is much stronger than if the wire was straight
- field lines parallel to axis of solenoid in the same direction
- uniform

Question 9

outside the solenoid

Answer 9

• magnetic field lines bend around from one end to the other of solenoid
• each field line is complete loop, because it passes through the inside of solenoid

Question 10

electromagnets

Answer 10

solenoid that has an iron core, current passed along wire magnetises the iron bar

Question 11

scrap yard crane

Answer 11

• vehicles lifted using powerful electromagnets attached to cranes
• steel sticks to magnet when current passes through the coil

Question 12

circuit breaker

Answer 12

• switch in series with an electromagnet
• when currents too large switch opens by electromagnet and stays open until manual reset

Question 13

electric bell

Answer 13

electromagnet attracts iron armature which opens at a switch

Question 14

the relay

Answer 14

current through coil of electromagnet magnetises the iron core which pulls armature onto the, this closes switch

Question 15

the motor effect

Answer 15

• force increased if current or strength of magnetic field or length of conductor is increased
• reversed if direction of current or magnetic field is reversed

Question 16

electric motor

Answer 16

electric motor coil turn when a current is passed through it

Question 17

magnetic flux density

Answer 17

a measure of the strength of a magnetic field
Force = magnetic flux density x current x length

Question 18

the generator effect

Answer 18

• the effect of inducing a potential difference using a magnetic field
• when a conductor crosses through the lines of a magnetic field a potential difference is induced across the ends of the conductor

Question 19

a generator test

Answer 19

• the faster a conductor crosses through the lines of a magnetic field, the bigger the induced potential difference
• when direct current electromagnet is used it need to be switched to induce a potential differnce

Question 20

direction of induced current

Answer 20

always opposes the original change that caused it