0 Members and 1 Guest are viewing this topic.

As I understand it, a changing magnetic field produces an electric field, and a changing electric field produces a magnetic field. This electromagnetic wave propagates through space at teh speed of light, as described by Maxwell's equations.A slowly changing magnetic field produces a smaller electric field, and a slowly changing electric field produces a smaller magnetic field.By this logic, the amplitude of a single photon would be proportional to its frequency.When you produce many photons of a single frequency, such as in a laser beam or a radio transmitter, the amplitude is proportional to the number of photons.

When you produce many photons of a single frequency, such as in a laser beam or a radio transmitter, the amplitude is proportional to the number of photons.

By this logic, the amplitude of a single photon would be proportional to its frequency.When you produce many photons of a single frequency, such as in a laser beam or a radio transmitter, the amplitude is proportional to the number of photons.

Quote from: evan_au on 17/08/2014 03:55:58By this logic, the amplitude of a single photon would be proportional to its frequency.When you produce many photons of a single frequency, such as in a laser beam or a radio transmitter, the amplitude is proportional to the number of photons.Yes, exactly! The classical wave that David Cooper mentioned is not a single photon. It is a collection of photons whose amplitude is proportional to the expected number of photons, which in turn is proportional to energy deposited on a detector if you were to take a measurement. If you were to write out a quantum wavefunction for a single photon, the amplitude would tell you the probability of finding a photon over a region of space. This is not the same as energy, since you can obviously have a range of anywhere from 0 to 1 probability of finding a photon independently of the photon frequency. (Though strictly speaking, you can't write out a quantum wavefunction for a single, pure photon, you can do so approximately in many cases).If you're interested in pursuing the details of how to build a classical wave from individual photons, you want to look up "quantum coherent state." The math can get ugly, but it describes how to build a classical wave from individual photons.

I don't know if a photon officially counts as a photon when it's travelling as a wave, but the shorter the wavelength (frequency of the light/radiation), the higher the energy it carries. However, that would not always apply if the amplitude of the wave could vary. What I'm wondering then it this: is the amplitude fixed in some way relative to the wavelength?

Quote from: David Cooper on 16/08/2014 18:43:12I don't know if a photon officially counts as a photon when it's travelling as a wave, but the shorter the wavelength (frequency of the light/radiation), the higher the energy it carries. However, that would not always apply if the amplitude of the wave could vary. What I'm wondering then it this: is the amplitude fixed in some way relative to the wavelength?It's always been my understanding that a photon doesn't have an amplitude. I just e-mailed David Griffiths to find out for you.

You are not alone! The problem is that you can't impose a classical macroscopic model on quantum reality: electromagnetic radiation behaves as it does, regardless of your model. The best we can achieve mathematically is two approximations to what actually happens, neither of which is a complete description. Whether you think of an elephant as a bulky herbivore or an intelligent manipulator, doesn't fully describe it, but if you want to keep one as a working animal, you need both approximations.