E3: Electrical energy — D level

When your family gets the electricity bill, it tells how many kWh (kilowatt-hours) you used. kWh is a measurement of energy.

You can work out how much energy an appliance uses with this formula:

E = Pt

E: Energy (in Wh – Watt-hours).

P: Power (in W – Watts).

t: time (in h – hours).

The electricity bill shows kWh. 1 kWh = 1000 Wh.

Here is a list of appliances you might have at home, and the power they use. Use this information for the questions that come after.

Air conditioner Bar heater LED light bulb Stove

2.5kW (2,500W) when cooling. 3.2kW (3,200W) when heating.

1,000W.

11W.

1,000W on one hotplate and 1,400W on the other hotplate.

Use the formula below to work out how much energy is used in these situations.

E = Pt

1. You turn on the bar heater for 2 hours. How much energy is used?
2. You leave your kitchen light on all day (12 hours). How much energy is used?
3. You cook some curried sausage on the 1,000W stove hotplate. It’s on for 30 minutes(0.5 hours). How much energy is used?
4. Your lounge room is freezing cold, so you use the airconditioner to warm it up. It takes 30 minutes (0.5 hours) to get warm. How much energy is used?

Final question:

Which appliances do you need to be the most careful about if you are trying to reduce your electricity bill?