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Current
Current = charge ÷ time (I = Q / t)
Resistance
Resistance = potential difference ÷ current (R = V / I)
Voltage
Voltage = current x resistance (V = I x R)
Power
Power = current x voltage (P = I x V)
Power (alternative formula)
Power = current² x resistance (P = I² x R)
Power (in terms of voltage)
Power = Voltage² / Resistance (P = V² / R)
Energy
Energy = power x time (E = P x t) or E = I x V x t or E = Q x V
Cost of electricity
Cost of electricity = number of kWh x cost per kWh
Resistance of a conductor
Resistance = constant × (length / cross-sectional area) (R = ρLA)
Current in Series Circuit
Same at all points in a series circuit.
Voltage in Series Circuit
Total potential difference across components = sum of the individual p.d.s (R = R1 + R2 + R3)
Current in Parallel Circuit
Sum of currents in branches equals total current entering/leaving parallel branch.
Voltage in Parallel Circuit
Potential difference across each branch is the same as the potential difference across the whole arrangement.
