Energy in the Home

This lesson covers the domestic use of energy, including power, energy calculations, kilowatt-hours, and reducing energy use in the home, as required by the Edexcel GCSE Physics specification (1PH0), Topic 3: Conservation of Energy. You need to be able to calculate energy costs and evaluate energy-saving measures.

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Power

Power is the rate at which energy is transferred (or the rate at which work is done). It tells you how quickly a device transfers energy.

The Equation

$P = \frac{E}{t}$P=tE​

Where:

• P = power (watts, W)
• E = energy transferred (joules, J)
• t = time (seconds, s)

Units

• 1 watt (W) = 1 joule per second (1 J/s).
• A 100 W light bulb transfers 100 J of energy every second.
• 1 kilowatt (kW) = 1000 W.

Exam Tip: Always check whether the question gives power in watts or kilowatts, and time in seconds or hours. Convert to consistent units before calculating.

Rearranging

Find this	Equation
Power	$P = \frac{E}{t}$P=tE​
Energy	$E = P \times t$E=P×t
Time	$t = \frac{E}{P}$t=PE​

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