Series and Parallel Circuits

Series circuits

Components in a single loop.

Current:   same everywhere          I₁ = I₂ = I₃
Voltage:   shared (adds up)         V = V₁ + V₂ + V₃
Resistance: adds up                 R = R₁ + R₂ + R₃

If one component breaks, all stop working.

Parallel circuits

Components on separate branches.

Current:   splits between branches  I = I₁ + I₂
Voltage:   same across each branch  V = V₁ = V₂
Resistance: total is LESS than the smallest branch

If one branch breaks, the others keep working (e.g. house lighting).

Worked example (series)

Two resistors 3 Ω and 5 Ω in series with a 16 V supply:

R = 3 + 5 = 8 Ω
I = V / R = 16 / 8 = 2 A

Exam tip

Series: current is the same, voltage shares. Parallel: voltage is the same, current shares. Adding resistors in parallel decreases total resistance.