3.17 Alternators, Dynamos & Oscilloscopes

Question 1

What are alternators and dynamos?

Answer 1

Generators

Question 2

How do alternators and dynamos generate electricity?

Answer 2

From rotational motion (e.g. rotating a coil of wire)

Question 3

What are the key differences between dynamos and alternators? (2)

Answer 3

• Dynamos have a split ring commutator, whilst alternators have slip rings and brushes.
• Due to the split ring commutator, dynamos produce direct current. Due to the slip rings and brushes, alternators produce alternating current.

Question 4

How do alternators work? (3)

Answer 4

• The coil of wire rotates relative to the magnets; this induces a magnetic field in the coil, which then induces a voltage and current in the coil.
• The slip rings and brushes mean that the contacts don’t swap every half turn (like they do in a motor or dynamo).
• This means that they produce an alternating potential difference and an alternating current (a.c.).

Question 5

How do dynamos work? (3)

Answer 5

• As the coil of wire spins relative to the magnet, a magnetic field, and hence a voltage and current, is induced in the coil.
• The split ring commutator means that the contacts swap every half turn.
• This means that they produce a direct potential difference and hence a direct current (d.c.). It’s called direct current because the current is always flowing in the same direction.

Question 6

What type of current is generated by a dynamo/

Answer 6

Direct current

Question 7

What do oscilloscopes show?

Answer 7

How the potential difference generated in a coil changes over time

Question 8

What happens to the oscillations on an oscilloscope when you increase the speed at which a coil rotates in an alternator?

Answer 8

The amplitude and the frequency both increase