Electronics Demonstrations page has demonstrations that use a Java applet that simulates electronic circuits. This is a pretty nice simple electronics circuit simulator that shows you clearly what happens on different electronics circuits. The movement of yellow dots indicates current flowing on the circuit. Check the demonstrations on the Electronics Demonstrations page and check also full applet that allows you to design your own circuits to simulate. This is really worth to look at if you are trying to learn electronics or how to use computer to simulate electronics circuits. falstad.com has also many other interesting educational Java applets for Mats, Physics and Engineering . Check for example Fourier Series Applet and Digital Filter Applet.