4.7.3.2 Uses of the Generator Effect (HT only)

Question 1

What is the generator effect used in?

Answer 1

• in alternator to generate ac
• in dynamo to generate dc

Question 2

How is the generator effect used in an alternator to generate ac?

Answer 2

• when the wire moves through the magnetic field the coil cuts magnetic field lines
• a p.d. is induced across the coil
• as there is a complete circuit a current is induced
• every half-turn the p.d. reverses direction
• so every half turn the current changes directions - alternating current
• as the 2 sides of the coil are attached to 2 different commutator rings an alternator produces and alternating p.d. and an alternating current (AC)

Question 3

What does a generator look like?

Answer 3

• coil of wire rotating in a magnetic field
• the coil is connected to 2 metal rings - commutators
• the commutators allow the current to pass out of the coil

Question 4

How does p.d. change in an alternator?

Answer 4

• when the coil is horizontal it is at maximum p.d.
  
  • at this point, the wire is cutting directly through the magnetic field lines at the fastest possible rate
• when the coil is vertical p.d. falls to 0 in alternator
  
  • as the coil is now parallel to the magnetic field so the coil is not cutting through the magnetic field lines
• p.d. is at lowest
  
  • as coil continues moving round p.d. has reversed direction as the 2 sides of the coil moving in different direction to which they were previously moving in

Question 5

Factors to increase the size of the AC in an alternator:

Answer 5

• (stronger magnet) increase strength of magnetic field - induce stronger p.d
• increase number of turns on coil
• increase area of coil
• increase rotation speed of the coil - increases both the size and frequency of the alternating current

Question 6

Graph of p.d. generated in alternator:

Answer 6

Question 7

Diagram of alternator:

Answer 7

Question 8

How is the generator effect used in a dynamo to generate dc?

Answer 8

• has 1 split ring commutator - split ring commutator has 2 sides separated by a gap
• side of coil moving up is connected to 1 side of the split ring commutator and the side of the coil that is moving down is connected to the other side of the split-ring commutator

Question 9

How does p.d. change in a dynamo?

Answer 9

• coil horizontal
  
  • as coil is cutting through the magnetic field lines a p.d. and current are induced
• coil vertical
  
  • moving parallel to magnetic field
  • not cutting through any field lines so p.d. is 0
• coil moved around
  
  • direction which the sides of the coil are moving is opposite to the direction which they were previously moving
  • the side of the coil moving down still connected to same side of split ring commutator
  • side of coil moving up still connected to same side of split ring commutator
  • so direction of p.d. and current does not reverse when coil rotates - d.c.

Question 10

Diagram of dynamo:

Answer 10

Question 11

Graph of p.d. generated in dynamo:

Answer 11

Question 12

Use of slip rings in alternator:

Answer 12

• provides continuous connection between coil and transformer
• stops wires twisting together

Question 13

Why does the handle of an alternator become much easier to turn when the alternator from the power supply becomes disconnected from transformer and lamp?

Answer 13

• no induced current
• no magnetic field
• to oppose movement of coil