Which of the following correctly defines the energy of a photon?

• A. E = mc^2
• B. E = hv
• C. E = P/V
• D. E = Fd

Answer: (B)

The energy of a photon is correctly defined by the equation E = hv, where E represents the energy of the photon, h is Planck's constant, and v (or sometimes expressed as f) is the frequency of the electromagnetic radiation. This relationship indicates that energy is directly proportional to the frequency of the photon, meaning higher frequency photons (like gamma rays) carry more energy than lower frequency photons (like radio waves).

This equation accurately describes the quantum nature of light, where photons are treated as discrete packets of energy. It also aligns with the principles of quantum mechanics, demonstrating how energy and frequency are fundamentally linked in the context of electromagnetic radiation.

The other equations provided do not describe the specific energy of a photon. For example, E = mc^2 is Einstein's famous equation relating mass and energy but does not specifically pertain to photons, which are massless. E = P/V describes the energy density in a different physical context, and E = Fd relates energy to mechanical work done by a force over a distance, which also does not apply to the energy of photons.