P5.1 Alternating Current

Question 1

What is direct current (d.c.)?

Answer 1

A current that flows in one direction only.

Question 2

What is alternating current (a.c.)?

Answer 2

A current that repeatedly reverses its direction.

Question 3

What is the frequency of UK mains electricity?

Answer 3

50 Hz (50 cycles per second).

Question 4

What is the live wire?

Answer 4

The live wire carries the alternating voltage into the appliance, changing from positive to negative each cycle.

Question 5

What is the neutral wire?

Answer 5

The neutral wire completes the circuit and carries the current back to the supply at around 0 V.

Question 6

What is the peak potential difference of UK mains?

Answer 6

About 325 V in each direction.

Question 7

How do step-up transformers help power stations?

Answer 7

They increase the voltage so the current becomes smaller, which reduces energy lost as heat in the cables.

Question 8

How do step-down transformers help consumers?

Answer 8

They reduce the voltage to safe levels for homes and appliances (e.g., 230 V).

Question 9

What does an oscilloscope show for an alternating potential difference?

Answer 9

It shows a wave that rises and falls repeatedly, crossing the zero line as the voltage changes direction.

Question 10

Why is less current useful for power transmission?

Answer 10

It reduces energy lost as heat in cables.