I just saw a video here about using neon bulbs to visualize microwaves in a microwave oven.
Another great microwave oven experiment (that I learned from Lynn Cominsky at Sonoma State) is measuring the speed of light (or the frequency of the microwaves emitted) using marshmallows.
1. Cut a bunch of marshmallows in half (or use small ones) and cover a plate with them.
2. Take the rotating platter out of the microwave and place the plate inside. The rotating platter helps cook your food evenly by spinning the food in and out of the microwave’s ‘hot spots’, but for this experiment we want the marshmallows not to cook evenly. The microwaves are emitted from one side of the microwave (where the emitter is located) and bounce off the opposite side, creating standing waves. The anti-nodes (crests) of the standing waves are the ‘hot spots’ I mentioned earlier. The marshmallows will burn along these anti-nodes.
3. Measure the distance between the burn marks. This distance is the wavelength of the microwaves emitted by your microwave.
4. Use this simple wave equation to verify either the speed of light (if your microwave lists its frequency on the back panel) or to determine the frequency of your microwave (given that the speed of light is approximately 3×10^8m/s).
Don’t forget to convert your units!