Why don't cell phones work in subways or subway tunnels?

Ever wonder why that when you walk into a subway tunnel your connection just shuts off. Well read this passage to find out. To fully understand the experiment you must first know what a cell phone is. Cell phones are actually a kind of small radio; they use a special kind of waves called radio waves. Radio waves are part of the electromagnetic spectrum. First let me explain what a wave is. A wave is a wave of energy having a frequency within the electromagnetic spectrum. For cell phones to work the people that are talking must be connected via antenna.

The antennas have different wave frequencies so that only the person that you want to talk to is on the line. (Ex. Frequencies are sort of like chat rooms, if you are in a private...