🔌 Circuits

How to Use It

Building

Click a piece in the tray, then click a square to put it there. It turns itself to meet whatever it is next to, so most of the time it just fits. Click the same piece again to turn it round yourself. Pick Throw away to take something off. The shaded squares are part of the puzzle and cannot be moved.

Flipping switches

Pick Flip — the pointing hand — and click a switch. Watch what happens to the bulb.

Open and closed

Electricity only goes round a loop with no gaps. A gap anywhere and nothing happens at all: that is an open circuit. Close every gap and it is a closed circuit, and it lights.

Why a bulb goes dim

Two bulbs in a row share the push, so each gets half the voltage — and a quarter of the power, which is why they look properly dim rather than half dim. Two bulbs side by side each get the whole push and both stay bright, but the battery has to work twice as hard.

Working a light from two places

The switch at the top of your stairs and the one at the bottom both work the same light. Neither of them makes a gap — each one sends the electricity down one of two roads, and the light is on when both happen to have picked the same road. An electrician calls that a three-way switch in America and a two-way switch in Britain: the same switch, named after its three terminals or after the two places it works from.

And from three places

For a third switch you cannot just add another one — you have to put a middle switch into both roads at once, which either lets them run straight past or swaps them over. Add as many of those as you like, and the light works from as many places as you like.

Short circuits

Electricity takes every road it can find, and takes the easy ones hardest. Lay a bare wire round a bulb and nearly all of it goes that way instead, leaving the bulb dark. Lay one straight across the battery and there is nothing to slow it down at all — the board turns red and tells you. That is what fuses are for.

Keyboard

Click the board, then use the arrow keys to move, Enter to place or flip, and R to turn a piece.