Domestic appliances and energy usage

What you will learn

Compare appliance power, use duration, duty cycle and energy consumption.

Specification mapping: C3.1

Prerequisites: C2.1.1, C2.1.3

Physical principles

To estimate an appliance’s energy use, combine its operating power with how long it runs. A high-power kettle used briefly may consume less energy than a modest-power device left on for many hours. Use measured average power or account for duty cycle where thermostats switch a heater, fridge or oven on and off.

Nameplate power is an operating rating, not a guarantee of continuous consumption. A monitor or plug-in energy meter can record actual accumulated energy. Include standby periods, changing settings and the relevant time interval. For a comparison, hold the required service constant, such as heating the same mass of water to the same temperature.

P = E/t supports comparisons in watts, seconds and joules. Domestic billing normally expresses electrical energy in kWh. Cost requires a supplied tariff; do not invent a current price. An appliance’s energy use alone does not establish total carbon emissions because the supply mix and system boundary also matter.

Scientific diagram and interpretation

Worked examples and applications

Common misconceptions

Power ratings alone do not rank total daily energy consumption.

Examination technique

Show power, operating time and duty-cycle assumptions separately.

For an explanation, connect the physical cause to its effect. For a calculation, state the model, rearrange before substitution, retain intermediate digits, and finish with units. For a data question, refer to the actual readings and distinguish a trend from proof of a cause.

Check your understanding

Five questions. Choose an option, then Check Answer. Read the feedback and use Try Again to reset. Use Tab between controls, arrow keys within radio groups, and Enter or Space on buttons. These local practice answers are not saved.