This java applet demonstrates standing electromagnetic waves in a 3-d rectangular box, or cavity resonator. To use the applet, double-click on one of the grid squares to select a mode. The TE modes are on top and the TM modes are on the bottom. Use the menu items to select the electric or magnetic field, and the way the field is displayed.

Full Directions.

Java Version.

Waveguide applet.

More applets.

Huge thanks to Bob Hanson and his team for converting this applet to javascript. The source.