How radio waves transmit energy

On the previous pages you saw that applying an electrical current to a wire creates radio waves, because the electrons in the wire emit photons. You learned that the electrons that travel through the wire emit photons, creating an electromagnetic field. And, when you apply an alternating current to the wire this creates and oscillating magnetic field, which generates a radio wave. Wow.

Now, that is all fine and dandy, but if we want to understand wireless communication like we see in wireless networks we have to know how information is transmitted by radio. In order to understand how that happens, we must first look at how an electromagnetic wave can transmit energy over a certain distance.

Excited electrons

Now, here comes the bit that's essential to radio communication. Electrons can emit photons, but they can also absorb photons. When an electron absorbs a photon it gets excited. Not literally. It doesn't go like 'weeeeee, I absorbed a photon'... Or maybe it does... What is most important is that the electrons that absorb photons will use the photon's energy to accelerate. They will be travelling the wire at a certain speed and once they absorb a photon that speed will increase. So, if you think about it, they are going like 'weeeee, I absorbed a photon'. It's like you (the photon) are pushing a child (the electron) of a slide.

The excited electrons will travel the metal they are in and create an electric current. Because that is what traveling electrons are: electric current.

That is how a radio wave can create an electric current in a metal object very far from its source. The radio wave encounters a metal object and the electrons in that metal object get excited by absorbing photons and start flowing through the metal object.

Car with antenna


This is why devices that use radio have antenna's. They need some metal object sticking out that receives radio waves.