Electrical Energy
Electrical energy consumed when charge Q moves through a potential difference V is E = VQ = VIt. Unit is the joule (J).
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Work done by current
When a charge Q moves through a potential difference V, the work done (energy transferred) is W = VQ. Since I = Q/t, we have Q = It, so the energy consumed in time t is E = VIt. This is the electrical energy converted (e.g. into heat or light) in a device.
Relation to power
Power P is the rate of energy transfer: P = E/t = VI. So E = Pt = VIt. For a resistor, using V = IR, we get E = I²Rt or E = V²t/R.
Units and practical use
Energy is in joules (J). Domestic electricity is often billed in kilowatt-hours (kWh): 1 kWh = 3.6 × 10⁶ J. Understanding electrical energy helps in comparing appliances and calculating cost.
Why is a kilowatt-hour a unit of energy and not of power?