In communication system EM waves are not interupted by objects why?

Question

Light waves are easily interupted by objects. In communication system EM waves are not interupted by objects why? Even in the closed room also we can get signals.

Answer 1

Gene is correct. In fact, the amount of penetration a radio signal has is in direct proportion with it's wavelength. Long waves (low frequency) penetrate matter to a greater degree then short waves (high frequency). The cost is that long waves take more power to generate, and they don't travel very far through space.

Microwaves can travel tremendous distances on very little power, but they are stopped cold by most solid objects. Wave expansion and reflection partially make up for this. Cell systems typically compensate for microwave's lack of penetration ability by having tower coverage that pretty much blankets every inhabited area. Even with all the towers out there, large buildings have to have internal signal boosters so that your phone will work indoors, away from windows.

At the other end of the spectrum, the Navy uses VLF (very low frequency) radio to communicate with it's submarine fleet, sometimes far below the surface of the ocean. To generate the extreme long waves, they use dipole antennas, many miles long and transmitters that use enough electricity to power a small city.

Answer 2

They get interrupted. Tune to an AM radio station and drive through a tunnel or a metal bridge and you'll lose them. To shield radio waves, the interrupting object must be a conductor and must be a significant part of the wavelength of the signal. You may notice your cell phone dropping in and out sometimes also. It's the same effect.