Hi, I'm Steve Jones and I'm going to tell you how a photon is produced. Now in an atom of course we have a nucleus but above the nucleus we have electrons. And it was discovered last century, the twentieth century that electrons can't have any levels, they can only have specific levels of energy. And we've called these E naught, E one, E two, E three, E four, E four is bigger than E naught. So what happens is the electrons can go from one energy to another as the material warms up. So the energy increases or decreases. Now when energy increases, you put energy in to the atoms by heating or doing something else. But when the electron, say in level two falls down in to E level one, we can see that there is a difference in energy. And the difference in energy here would be E two minus E one. So there is a change in energy. That energy is lost. So where does it go? And the answer is, it goes in to a photon. So a drop in level, say from E four to E three, the energy associated with that is E four minus E three and this gives a packet of energy which we call a photon which described as HU. H is a constant called Plank's constant after a gentleman called Plank. And U is the frequency. This photon is in fact electromagnetic, electromagnetic radiation and in fact is or can be light, visible light. So the electron can actually glow and give out a visible light. It might b  X-rays, it might be infrared, it might be ultraviolet. It can be any of the electromagnetic radiations. But the photon depends on how big the change is. And the changes can be of all different energy. So it will give out all different wave lengths and frequencies and all different types of light. So briefly that is how a photon is produced.
