Energy Transferred in Circuits

This lesson covers the calculation of energy transferred in electrical circuits, including the use of kilowatt-hours and electricity bill calculations, as required by the Edexcel GCSE Combined Science specification (1SC0).

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Energy Transferred — Two Key Equations

Equation 1: E = Pt

$E = Pt$E=Pt

where:

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

This equation is a rearrangement of the power equation $P = E/t$P=E/t.

Equation 2: E = QV

$E = QV$E=QV

where:

• E = energy transferred in joules (J)
• Q = charge in coulombs (C)
• V = potential difference in volts (V)

This equation comes from the definition of potential difference: $V = E/Q$V=E/Q.

Equation	Best used when you know...
$E = Pt$E=Pt	Power and time
$E = QV$E=QV	Charge and voltage

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Worked Examples Using E = Pt

Worked Example 1

A 2000 W kettle is switched on for 3 minutes. How much energy is transferred?

Convert time: $t = 3 \times 60 = 180 \text{ s}$t=3×60=180 s