Chapter 18: AC

Question 1

RMS current

Answer 1

value of an alternating current is the value of steady current that will dissipate heat at the same average rate as the AC in a resistive load

Question 2

Explain what is meant by an ideal transformer

Answer 2

An ideal transformer is one that is 100% efficient and has no energy losses

Question 3

State two reasons why soft iron, which is easily magnetised and demagnetised. is used as the core for transformers

Answer 3

1. Soft iron is easily magnetised and demagnetised, such that there is no time delay for induction between the primary and secondary coil.
2. Soft iron is highly permeable to magnetic flux density

Question 4

Why is a high voltage used in the transmission of electrical power in AC

Answer 4

Power loss in transmission cables NOT negligible due to high resistance, hence high voltage transmission needed to minimise power loss

High voltage output from generator working at a constant power, current output
I = P/V becomes smaller. Power lost as heat in the transmission cable of a fixed
resistance = I^2 R will be smaller.

Question 5

Advantage of alternating voltage

Answer 5

AC voltages can be stepped up and down using a transformer for more efficient transmission of power