Imagine that you have a box with several light bulbs and on-off switches on it. Inside the box is a battery connected to the switches and light bulbs in some way (it doesn't necessarily use all the switches or light bulbs), and no other components are inside the box. I have implemented this in a web page using quite a lot of Javascript. The page includes over 20 different circuit puzzles of varying degrees of difficulty, and includes provision for 'unscrewing' the bulbs, as well as turning the switches off and on.

In addition, there is a circuit emulation section, where you can build up a circuit of components to emulate the puzzle. Once you think you have a solution you can test it. There is a help page which explains how to use all the features.

Note: For this circuit page to work you must have Javascript enabled, and be using version 4 or later of Internet Explorer or Netscape.

Go ahead - give it a try! - it will open in a separate window.