I’m currently studying for my amateur radio Foundation license, and as part of this I’ve been playing about with electronics a bit – something which I never really learnt properly when I was younger.
A few weeks ago I stumbled across the personal site of Paul Falstad, and his amazing array of maths and physics Java applets. Covering acoustics, signals processing, electrodynamics and even quantum mechanics, there’s bound to be something there to keep your entertained for far longer than is probably appropriate.
The Analogue Circuit Simulator (warning: Java applet will start straight away) is the one that’s sucked up most of my time – it’s full of features and examples, and is easy to use. It allows you to see the voltages and currents at all parts of the circuit, and even has scopes so you can watch values change over time.
As well as that, I’ve also found the 2D Electrodynamics applet useful for visualising how electromagnetic waves propagate.
Give them a try, although I’m not responsible for the amount of time you’ll inevitably lose doing so…