Electromagnetism

Question 1

Domain

Answer 1

Area inside a magnetic metal that can be thought of as a mini magnet within the structure

Question 2

Flux density

Answer 2

Strength of magnetic field in a volume of space

Question 3

Induced magnetism

Answer 3

Magnetism produced in a magnetic material by a permanent magnet or electromagnet

Question 4

Induction

Answer 4

A potential difference produced when the flux passing through a conductor changes

Question 5

Magnetic field

Answer 5

Area around a magnet where it will produce a force on another magnet or magnetic material. Points from north to south

Question 6

Motor effect

Answer 6

Force produced on a conductor carrying a current placed at right angles to a magnetic field

Question 7

Solenoid

Answer 7

A coil of wire carrying a current. Produces a magnetic field with the same shape as a bar magnet

Question 8

Tesla

Answer 8

The unit used to measure flux density

Question 9

Magnetic fields

Answer 9

Lines point from north to south around a bar magnet, strongest near the poles
Attract where the lines join up, repel when they don’t

Question 10

Field around the wire

Answer 10

Has a circular magnetic field around it

Use right hand grip rule where thumb points in direction of current

Question 11

Magnetic metals

Answer 11

Iron
Cobalt
Nickel

Question 12

Force on a conductor

Answer 12

F=BIL
F= force in Newtons
B= flux density in Tesla
I= current in Amperes
L= length in metres

Question 13

Motor effect

Answer 13

Two permanent magnets with a coiled wire between them carrying a current makes the wire spin

Question 14

Fleming’s left hand rule

Answer 14

Thumb= F
Finger 1= B
Finger 2= I
All at right angles

Question 15

Factors which increase induction

Answer 15

Increase flux density
More coils
Closer to the wire
Increased current

Question 16

Speakers

Answer 16

Pass an alternating current through a coil in a permanent magnetic field. As current changes direction, coil attracts/repels

Question 17

Microphones

Answer 17

Sound waves make diaphragm and coil vibrate backwards and forwards in a magnetic field. Induces a potential difference causing an alternating current

Question 18

DC Motors

Answer 18

Current flows through coil
Motor effect produced a force
Motor has a split ring commutator which means current flows the same way relative to magnetic field

Question 19

DC Dynamo

Answer 19

Coil is spun in the magnetic field
Induces potential difference
Coil has a split connection so the current will be a varying direct current
Maximum every 108 degrees

Question 20

AC Alternator

Answer 20

Coil is spun in the magnetic field
Induces potential difference
As the connections to either side of the coil are permanent the current changes direction with every 180 degree turn

Question 21

What do transformers work on?

Answer 21

Alternating current

Question 22

Transformers

Answer 22

Laminated core made from iron, 2 coils on opposite sides
Step-up have more turns on secondary than primary, step-down the opposite
Changes size of alternating voltage
Step up turns power stations to grid, step down grid to home (230V)

Question 23

Summary

Answer 23

Faster movement increases induced p.d.
Increasing length of wire increases induced p.d.
Stronger field increases induced p.d.
Changing direction of field reverses induced p.d. direction

Question 24

Generator Effect

Answer 24

When moving magnetic field lines pass through a conductor (or a moving conductor passes through a magnetic field) a p.d. is induced in the conductor

Question 25

2x speed=

Answer 25

2x p.d.

Question 26

What happens as you go up the electromagnetic spectrum?

Answer 26

Increased frequency and wavelength

Decreased energy

Question 27

How to answer motor effect questions

Answer 27

1. Current flows around the circuit
2. Creates a temporary magnetic field
3. Interacts with the permanent magnetic field of the magnet
4. Creates a force which turns the coil
5. In the direction shown by fleming’s left hand rule

Question 28

Brushes

Answer 28

Conduct current between stationary wires and rotating wire of motor

Question 29

Commutator

Answer 29

Reverses the current every half turn to ensure motor turns continuously

Question 30

Relay switch

Answer 30

Press the switch causing a current to flow, turn on very large currents safely

Question 31

Circuit breaker

Answer 31

When the current is too high, electromagnet becomes magnetised and stops the flow to a section of the circuit

Question 32

Transformers exam questions

Answer 32

1. Either steps-up or steps-down the voltage
2. Induces a magnetic field
3. Current is alternating, causing changing magnetic field in the iron core
4. Core strengthens the magnetic field
5. Field lines interact with secondary coil, inducing a voltage or secondary cell

Question 33

Magnetically soft

Answer 33

The magnet can be switched on and off

Question 34

Magnetically hard

Answer 34

A permanent magnet

Question 35

Plotting compass bar

Answer 35

Place the compass at one pole and draw where it points continuing until you reach the other pole, repeat going the other direction (top/bottom)

Question 36

Plotting compass solenoid

Answer 36

Place the compass at one point on the wire
Turn the power supply on and off
Move it further along and turn on and off again
Move further away to see the weakening