Resistance: Calculations in Electric Circuits

Current in a series circuitThe current is the same at every point along the wire

Current in a parallel circuit Different-sized currents can flow through parallel parts of a circuit The current before and after the parallel section of circuit is the same

The sum of the currents entering a point in a circuit equals the sum of the currents leaving it I = I₁ + I₂ + ...

Voltage in circuits The potential difference of the full circuit equals the sum of all the potential differences in the circuit V = V₁ + V₂ = ...

Resistance in circuits

Resistors in series:R = R₁ + R₂Derivation: Based on V = V₁ + V₂ The two resistors are connected in series, so the same current flows through both IR = IR₁ + IR₂ (Since V = IR) R = R₁ + R₂ (by dividing by I)

Resistors in parallel1/R = 1/R₁ + 1/R₂Derivation Based on I = I₁ + I₂ The potential difference between two points is the same regardless of the path followed (=V) V/R = V/R₁ + V/R₂ (since I = V/R ; Ohm's law) 1/R = 1/R₁ + 1/R₂ (by dividing by V)

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