Power and Energy Transfer in Circuits

This lesson covers electrical power and energy transfer in circuits, including the key power equations and the calculation of energy in joules and kilowatt-hours, as required by AQA GCSE Combined Science Trilogy (8464, section 6.2.1).

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What Is Electrical Power?

Power is the rate of energy transfer — how quickly energy is transferred from one form to another.

Power is measured in watts (W). One watt is one joule per second:

$1 \text{ W} = 1 \text{ J/s}$1 W=1 J/s

Higher power = faster energy transfer.

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Power Equations

AQA requires you to know and use three power equations:

Equation 1: P = IV

$P = I \times V$P=I×V

Where:

• $P$P = power in watts (W)
• $I$I = current in amperes (A)
• $V$V = potential difference in volts (V)

Equation 2: P = I²R

$P = I^2 \times R$P=I2×R

Where:

• $P$P = power in watts (W)
• $I$I = current in amperes (A)
• $R$R = resistance in ohms (Ω)

This equation is derived by substituting $V = IR$V=IR into $P = IV$P=IV:

$P = I \times (IR) = I^2R$P=I×(IR)=I2R

Equation 3: P = V²/R