I want to grasp the idea of a photon.
While researching, I have come upon many different ways of describing a photon, but have found "quantum of the electromagnetic field" to be most satisfying. However, I still have a few questions about this description.
I. What does 'quantum' mean in this context? Quantum of what physical quantity?
II. What features do photons exhibit as a wave? (wavelength, speed, et cetera)
III. What features do photons exhibit as a particle? (mass, spin, et cetera)
I would especially thank if anyone could explain the momentum of a photon as a wave and as a particle.
For anybody wondering, I am a high school student interested, but not fluent in physics.
Best Answer
Photons of frequency $\nu$ have energy $E = h\nu$. This means: if a photon of this frequency is absorbed or emitted, exactly this amount (quantum) of energy is transferred.
Photons of frequency $\nu$ have momentum $p = \frac{h\nu}{c}$. This means: if a photon of this frequency is absorbed or emitted, exactly this amount (quantum) of momentum is transferred. Photons move in the direction of their momentum vector.
Circularly polarized photons have angular momentum $\ell_z=\pm \hbar$. This means, if they are absorbed or emitted, exactly this amount (quantum) of angular momentum is transferred.
As a wave they have frequency $\nu$ and wavelength $\lambda$, related by $$ \nu\lambda = c,$$ where $c$ is the speed of light. The speed of light is the same in all inertial frames of reference. As a wave they also have an amplitude.
As waves they can interfere (e.g. double slit experiment), be reflected from mirrors, be transmitted through matter.
The particle properties of photons are energy, momentum, and angular momentum. They have zero rest mass. Their spin (angular momentum) depends on their polarization, but it is integer, so they are bosons. As particles, they can, for example, hit objects and exert pressure. They can be emitted and absorbed transferring discrete portions of energy, momentum, and angular momentum.