Which statement correctly describes the mass of a photon?

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Multiple Choice

Which statement correctly describes the mass of a photon?

In relativity, photons are massless in terms of rest (invariant) mass, yet they carry energy and momentum. The relationship E^2 = (pc)^2 + (m0 c^2)^2 shows that if a particle’s rest mass m0 is zero, then E = pc, which is exactly how a photon behaves. This means photons travel at the speed of light in vacuum and cannot be at rest. They do not have rest mass, even though they can transfer energy and momentum to objects they interact with. Therefore, saying photons have no mass reflects their zero rest mass. The fact that light slows in a medium is due to interactions with the material (dispersion and the medium’s refractive index), not because photons acquire rest mass. The other statements imply nonzero rest mass, being mass only in a medium, or negative mass, which contradicts the established physics of photons.

In relativity, photons are massless in terms of rest (invariant) mass, yet they carry energy and momentum. The relationship E^2 = (pc)^2 + (m0 c^2)^2 shows that if a particle’s rest mass m0 is zero, then E = pc, which is exactly how a photon behaves. This means photons travel at the speed of light in vacuum and cannot be at rest. They do not have rest mass, even though they can transfer energy and momentum to objects they interact with.

Therefore, saying photons have no mass reflects their zero rest mass. The fact that light slows in a medium is due to interactions with the material (dispersion and the medium’s refractive index), not because photons acquire rest mass. The other statements imply nonzero rest mass, being mass only in a medium, or negative mass, which contradicts the established physics of photons.

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