Key Stage 3 (KS3) Energy Practice Test

The formula to calculate the amount of energy transferred by an appliance is based on the relationship between power, which is the rate at which energy is used, and time. Energy transferred is measured in joules (J), and the correct way to express this relationship is through the equation: Energy transferred (J) = Power (W) x Time (s).

In this equation, power is measured in watts (W), where 1 watt is equal to 1 joule per second. Therefore, multiplying power by time (in seconds) gives the total energy consumed or transferred over that period. This is fundamental to understanding how electrical appliances work, as knowing the power rating of an appliance together with the time it is in use allows one to calculate the total energy consumed.

The other choices present alternative units or formats that do not accurately represent this relationship. Using kilowatts and hours is valid but requires a conversion into joules if one needs the energy in joules instead of kilowatt-hours. Similarly, using minutes or joules as the unit of power does not align with the standard calculation for energy in joules that incorporates seconds for time. Using kilojoules also introduces confusion in unit conversion when not aligned properly with the power unit used.