Christmas Lights: Series vs Parallel Circuits (2D Schematic)

Wiring

Click a bulb symbol on the diagram to burn it out (or repair it). Drag to pan, scroll to zoom.

Circuit Parameters

Number of bulbs N 8

Source voltage V_s 12.0 V

Bulb resistance R 20 Ω

Live Circuit Readouts

Total resistance

160.0 Ω

Total current

75.0 mA

V per bulb

1.50 V

Total power

0.90 W

The real physics

Each bulb symbol is a resistor of resistance R. In series the diagram draws one closed loop, so Kirchhoff's current law forces the same current I through every bulb: I = V_s/(N·R). Kirchhoff's voltage law then splits the source EMF evenly across the loop, so each bulb only gets V_s/N. Click any bulb to open that node of the loop — the whole loop breaks, current drops to zero everywhere, and every bulb in the diagram goes dark at once.

In parallel the diagram draws two rails (a "ladder"), with each bulb its own rung directly across both rails. Kirchhoff's voltage law then gives every intact bulb the full V_s, no matter how many other rungs exist or how many have been clicked dark — removing one rung doesn't change the voltage across the rest. Kirchhoff's current law says the source only has to supply the sum of the surviving branches' currents, so total resistance drops as bulbs are added.

Series:   R_tot = N·R        I = Vs/R_tot        V_bulb = Vs/N        P_bulb = I²R
Parallel: R_tot = R/N_active  I_bulb = Vs/R        V_bulb = Vs          P_bulb = Vs²/R

Mode: Series · bulbs lit: 8/8

Drag to pan · scroll to zoom