Unit 1: 3 - Electrical Energy

Question 1

What is an electrical appliance?

Answer 1

A machine that transfers electrical energy into a useful form of energy that we need (e.g. A lamp, speakers, television etc.).

Question 2

What is the unit of power?

Answer 2

Watts, W.

Question 3

What is the equation for power?

Answer 3

(On the formula sheet)

P (W) = E (J) / t (s)

Question 4

How to we measure the amount of energy that a household uses?

Answer 4

Kilowatt-hour (kWh), the amount of energy that would be transferred by a one-kilowatt device when used for an hour.

Question 5

How do we work out the amount of energy transferred to a mains appliance?

Answer 5

E = P * t

Energy transferred (kWh) = Power of the appliance in kilowatts (kW) * time taken (in hours)

Question 6

What must we consider when comparing the cost effectiveness of devices?

Answer 6

• The cost of buying the appliance;
• The cost of installing the appliance;
• The running costs;
• The maintenance costs;
• The enviromental costs;
• (The interest charged on a loan to buy the appliance).

Question 7

What is payback time?

Answer 7

The time it takes for an appliance or insulation to pay for itself in terms of energy savings.