Simple circuits

Pro-Tip. No closed loop, no light. A short skips the bulb.

Current needs a closed loop. It leaves one side of the battery, goes through the load, and comes back to the other side. An open switch breaks the loop, so the bulb stays dark. Push the button and the loop closes.

A short is a path around the load. The current takes that easy wire and skips the bulb, so the bulb does not light. In series, one path feeds every bulb. In parallel, each bulb has its own path back.

Closed loop. The pushbutton is in. Current flows, and the bulb lights.

Open. The button is out, so the loop is broken and the bulb is dark.

Short. A wire jumps around the bulb. Current skips the bulb.

Series. One path, two bulbs. Open either one and both go dark.

Parallel. Each bulb has its own path. One can be dark while the other stays lit.

Worked example

Two bulbs are in parallel. One bulb burns out.

The other bulb stays lit. Each one has its own path back to the battery.

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