# Question on how a radio transmits

1. Nov 2, 2005

### BigMacnFries

My understanding of EM wave emission on a particle level is that when an electron jumps to a lower energy level it emits a photon. The probability of where you will find this photon is described by a wave, so when you have a lot of photons you are safe to treat light as a wave (in most circumstances).
Radios work under frequency modulation or amplutude modulation. Say for amplutude modulation the frequency is constant and the strenght of the EM wave is varied. Does this mean on an emmission level the atoms in the metal are simultanously emitting a large amount of photons one microsecond then not as many photons the next microsecond. I am confused as to what goes on inside an antenna when a signal is transmitted.

2. Nov 2, 2005

### ZapperZ

Staff Emeritus
But this is NOT the only way to produce EM radiation. Put a bunch of electrons in a ring and make it go round and round, and you will also get EM radiation. Or make the electrons jiggle up and down. You get the same.

Accelerated charges radiate. This is the principle being used in antenna transmission. At the simplest and most naive case, you have current oscillating in an antenna, thus charges oscillating back and forth.

Zz.

3. Nov 2, 2005

### BigMacnFries

Do charges emit when the deaccelarate, accelerate or both?

4. Nov 2, 2005

### Integral

Staff Emeritus
Both, the only difference between the two is a negative sign.

5. Nov 2, 2005

### BigMacnFries

In a radio antenna is it the free electrons in the metal that move around in systematic ways to create the transmission, if so how do they move?

6. Nov 2, 2005

### ZapperZ

Staff Emeritus
In metals (and antenna are usually made of metals), the "free" conduction electrons are the only ones that can move. How they move? Via the applied potential, the same way the AC current in your household wires moves.

Zz.