Although photons are most commonly thought of in the context of light waves, which are a form of electromagnetic wave, they comprise all forms of electromagnetic waves. As stated in the Wikipedia writeup on "Electromagnetic Radiation":
However, in contrast to assertions Geoff has made in some past threads, in the case of electrical signals being conducted via wires the electromagnetic waves which convey the energy of those signals from source to destination, and which are comprised of photons, and which propagate at a substantial fraction of the speed of light in a vacuum (in contrast to the vastly slower movement of electrons), DO NOT travel within the conductors. They travel primarily within the dielectric (i.e., the insulating material) surrounding the conductors.
A consequence of that is that the propagation velocity of signals being conducted by various cables depends mainly on the "dielectric constant" (aka "relative permittivity") of the insulation that is used in the particular cable, the variation typically being within a range of 50% to 95% or so of the speed of light in a vacuum. As stated in the Wikipedia writeup on "Velocity Factor":
-- Al
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space-time, carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.
However, in contrast to assertions Geoff has made in some past threads, in the case of electrical signals being conducted via wires the electromagnetic waves which convey the energy of those signals from source to destination, and which are comprised of photons, and which propagate at a substantial fraction of the speed of light in a vacuum (in contrast to the vastly slower movement of electrons), DO NOT travel within the conductors. They travel primarily within the dielectric (i.e., the insulating material) surrounding the conductors.
A consequence of that is that the propagation velocity of signals being conducted by various cables depends mainly on the "dielectric constant" (aka "relative permittivity") of the insulation that is used in the particular cable, the variation typically being within a range of 50% to 95% or so of the speed of light in a vacuum. As stated in the Wikipedia writeup on "Velocity Factor":
In electrical cables, the velocity factor mainly depends on the insulating material ....Regards,
VF equals the reciprocal of the square root of the dielectric constant (relative permittivity) ... of the material through which the signal passes.
-- Al