Electrical power

Question 1

What is electrical power?

Answer 1

Electrical power is the rate of energy transfer. It is measured in watts (W). One watt is one joule per second.

Question 2

How do you work out power?

Answer 2

power (w) = energy transferred (j) / time (s)

Question 3

How do you work out electrical power?

Answer 3

electrical power (w) = current (A) x potential difference (V)

Question 4

What is a fuse?

Answer 4

A fuse is a very thin piece of wire that acts as a safety device in a mains plug.

Question 5

What do you do to find the correct fuse to use?

Answer 5

You have to calculate the normal operating current for an appliance. You can do this by:
power = current x potential difference
current = power / potential difference

Question 6

How is the cost of electricity calculated?

Answer 6

cost (p) = power (kW) x time (h) x cost per kW h (p/kW h)

Question 7

Give 4 examples of energy-saving devices:

Answer 7

• compact fluorescent bulbs
• motion-activated lights
• home insulation
• standby detection devices

Question 8

How do you work out payback time?

Answer 8

payback time = initial cost / annual saving

Question 9

What will installing double glazing do?

Answer 9

Installing double glazing will provide better soundproofing or increase the sale-ability of a home.