What term describes a particle of electromagnetic radiation that has zero mass and carries a quantum of energy?

• A. Photon
• B. Ground state
• C. Excited state
• D. Line-emission spectrum

Answer: (A)

Light can be described as consisting of particles called photons. A photon is a massless particle that carries energy in discrete units, or quanta. Its energy is given by E = hν (or E = hc/λ), so each photon is a packet of energy associated with a particular frequency or wavelength. Because photons have zero rest mass yet carry energy and momentum, they fit the description of a particle of electromagnetic radiation that carries a quantum of energy.

Ground state and excited state refer to the energy levels of electrons within atoms, not to a particle of light. A line-emission spectrum describes the specific wavelengths released by transitions between those energy levels, again describing the light rather than a light quantum itself.