End Of Unit Questions

Question 1

How may energy be wasted in an electrical heater?

Answer 1

As light from the glowing filament

Question 2

How may energy be wasted in an electrical kettle?

Answer 2

Heating the body of the kettle itself and also possibly sound

Question 3

How many kilowatts are equivalent to 30,000watts?

Answer 3

30 kW

Question 4

Which is more powerful, a 2000W hairdryer or a 2.2kW hairdryer?

Answer 4

2.2kW hairdryer

Question 5

What quantity is measured in kilojoules?

Answer 5

Energy is measured in kilojoules

Question 6

An electrical light bulb transfers 6000J of energy in 1 minute. What is its power?

Answer 6

100W

Question 7

How much electrical energy in kWh is transferred when a 2kW iron is used for 30 minutes?

Answer 7

1kWh

Question 8

Why is the electrical energy supplied by the mains measured in kWh?

Answer 8

The joule is too small to be useful in this situation

Question 9

A machine has an input power rating of 100kW and a useful power output of 40kW. What is its percentage efficiency?

Answer 9

40%

Question 10

Electricity costs 12p per kWh. What is the cost of using a 2.5 kW heater for 2 hours?

Answer 10

60p

Question 11

It costs 6.6p to use a 1.2kW microwave oven for 30 minutes. What is the cost per kWh of the energy supplied?

Answer 11

11p

Question 12

What is the useful energy transfer in an electric toaster?

Answer 12

Electrical to heat