Electromagnetic induction

Question 1

What is electromagnetic induction

Answer 1

The induction of a potential difference (and current if there’s a complete circuit) in a wire that is experiencing a change in magnetic field

Question 2

Describe current induction

Answer 2

1. Current is induced if a wire is moved in a magnetic field
2. The wire forms a potential difference (electrons move to one side of the conductor as the field changes)
3. If the wire is connected in a circuit, a current will flow

Question 3

Describe current induction on a small scale

Answer 3

Spinning a coil of wire in between two permanent magnets will cause a current to flow in the wire

Question 4

Describe current induction on a large scale

Answer 4

1. Water is heated up to form steam
2. Steam is put under pressure into a turbine
3. Turbine rotates which is connected to a generator (massive wire coil)
4. Current is generated in the coil by the spinning motion of the coil through the field

Question 5

What factors affect the size of the current/voltage produced

Answer 5

• Number of coils in a wire
• Speed of rotation
• Magnetic field strength

Question 6

How is electromagnetic induction used in alternators

Answer 6

Every half turn the current switches direction as the wire would be in the opposite direction compared to it’s starting position

Question 7

How is electromagnetic induction used in Dynamo

Answer 7

1. Generators apply a force to rotate a coil in a magnetic field
2. As the coil spins a current is induced which changes direction every half turn
3. Dynamos are d.c generators that contain a split-ring communicator
4. This swaps every half tern keeping the current flowing one direction

Question 8

How does a loudspeaker work

Answer 8

1. A coil is wrapped around one poile of a permanent magnet so a.c signal causes a force
2. When the current is reversed the force acts in the opposite direction
3. Movements make the cone vibrate which creates a soundwave

Question 9

How does a microphone work

Answer 9

1. Sound waves hit a flexible diaphragm attached to a coil of wire
2. The coil surrounds one pole of a permanent magnet and is surrounded by another pole
3. diaphragm and coil move causing a current
   4/ Louder sounds cause more movement

Question 10

How do transformers work

Answer 10

Alternating current in first coil creates a changing magnetic field
Changing field cuts into secondary coil which is also AC

Question 11

Describe a step up transformer

Answer 11

More coils on secondary coil - voltage will be increased and will have a large induced potential difference (contains a lower primary voltage)

Question 12

Describe a step down transformer

Answer 12

Fewer coils on secondary coil - reduces the voltage of an alternating current (AC) power supply.
- smaller potential difference

Question 13

What is the turns ratio equation for transformers

Answer 13

no. of coils on primary / no. of coils on secondary
= p.d of primary / p.d of secondary

Question 14

Why is electrical energy transferred at high voltages from power stations using step up transfromers

Answer 14

To transmit huge amounts of power - high p.d or high current is needed
Wires heat up causing energy to dissipate to surroundings
Step up transformers increse p.d and decrease current to make it more efficient

Question 15

Why is electrical energy transferred at low voltages domestically using transformers

Answer 15

Step down transformers bring the p.d down to safe usable levels for customers