Q. Why does where I stand in my room affect my FM reception?

Boston

A. This phenomenon is called multipath. After a radio signal leaves the transmitter, it starts hitting metal everywhere and bouncing around. Your radio is actually receiving the signal from lots of directions.

The signal has no trouble passing through non-conducting materials like wood and glass. But the human body, made of so much salty water, is a good conductor. As you move around in the room, you interfere with some of the multiple signals coming in from outside.

But you only deflect a signal that's the right size: FM. From peak to trough, half a cycle, an average FM wave is only five feet. A person five feet tall is enough to interfere with a wave that size. But we don't make much of a dent in a 1,000-foot AM wave, most of which still gets to the radio.