Physics - Communication with Transverse Waves

One difficulty with using these electromagnetic waves for communication is that they travel in straight lines. This can cause problems because the surface of the Earth is curved. For the longer waves, like radio, this is not a massive issue because these waves can be reflected and they also diffract. Diffraction is the spreading out of a wave when it passes through a gap or around an object. The gap or object needs to be about the same size or smaller than the wavelength for diffraction to occur.

Radio waves can travel long distances because they can be reflected round the curvature of the Earth. They reflect off the ionosphere (a layer of the Earth's atmosphere) and off the surface of the Earth itself. Each time a wave is reflected it loses a little energy. This means that radio signals get weaker the further you are from the transmitter. It is for that reason that repeater stations are built which boost the signal strength and quality.

Radio waves can also travel round corners because of diffraction and can reach people in the bottom of valleys. It works because hills are comparable in size to the wavelength of radio waves. Diffraction allows radio signals to reach people who are not in direct line with the transmitter. The deeper and narrower the valley, the more difficult it is for them to receive a radio signal that is not coming from directly above.

As any owner of a mobile telephone will know, there are places where you can't get a signal. This is because they work using microwave technology. Microwaves have a much shorter wavelength than radio waves and so don't diffract as easily. They are also blocked more easily than radio waves which is why sometimes you need to move around a building or go outside to find the best signal.