Why does a microwave oven make a bulb light up?

Dear Straight Dope: I heard a rumour once that if you put a light bulb (60w) into a microwave oven, in a bowl of water (just covering the metal), that the light would come on! Well, being the nut that I am, I tried it. To my surprise, the rumour was right! The light flickered on! I couldn’t believe it! My question is ... how did that happen? I know you need some kind of current ... so how is that created? Matt Steeves, Moncton, NB, Canada

Mac replies:

This one is actually quite simple. Microwave ovens work by bombarding food with radio waves, right? And what happens when a radio wave goes past an antenna? You get a current through it. With me so far? Well, as far as the microwaves (the waves, not the oven) are concerned, the water and the filament and wires in the bulb are as good an antenna as any. You might ask (go ahead … ask. You know you want to), “how does the electricity flow, if it has no ground?” The answer is, “induction, and microwaves going in every possible direction.” One part of the wire might be getting zonked while another isn’t, and even wire can store some static charge. The point is, the fluctuating magnetic field created by the microwave oven induces a current to flow, so the bulb lights up.

Mac

Send questions to Cecil via cecil@straightdope.com.

STAFF REPORTS ARE WRITTEN BY THE STRAIGHT DOPE SCIENCE ADVISORY BOARD, CECIL’S ONLINE AUXILIARY. THOUGH THE SDSAB DOES ITS BEST, THESE COLUMNS ARE EDITED BY ED ZOTTI, NOT CECIL, SO ACCURACYWISE YOU’D BETTER KEEP YOUR FINGERS CROSSED.

Why does a microwave oven make a bulb light up?

A STAFF REPORT FROM THE STRAIGHT DOPE SCIENCE ADVISORY BOARD