Expert: Dave Nyce - 4/8/2003

Question
I am doing a science  project for my eight grade class next week.   I am interested in just why a light bulb placed in a glass of water  will light up when placed into a micro wave oven.  And the oven turned on.  What engercy does the microwave have on it.  Thank you Ken

Answer
The microwave energy is electromagnetic energy with a frequency of over 1 GHz, that means it has more than 1 billion cycles per second.

The filament of the light bulb is a tungsten wire, which is an electrical conductor. The electric field of the electromagnetic (microwave) energy causes electricity to flow within the filament wire. This heats it up so that it can glow. It is similar to the problem you have when you place something metal into the microwave and it makes sparks (don't put metal items in the microwave because this can damage the oven).

The water is just there in your experiment to provide a load for the microwave source, and prevent damage.

Hope this helps!

Dave