X-ray photon energy is inversely related to wavelength.

• A. Directly proportional to wavelength
• B. Inversely proportional to wavelength
• C. Not related to wavelength
• D. Proportional to the square root of wavelength

Answer: (B)

Photon energy is determined by how much energy a single photon carries, which is given by E = hν, where h is Planck’s constant and ν is frequency. The frequency relates to wavelength by ν = c/λ, with c as the speed of light. Put together, E = h c / λ. This shows energy is inversely proportional to wavelength: shorter wavelengths mean higher energy, longer wavelengths mean lower energy.

In X-ray terms, shorter-wavelength photons are more penetrating and carry more energy per photon, while longer-wavelength photons carry less energy. The other statements would either imply energy increases with wavelength, has no relation to wavelength, or grows with the square root of wavelength, all of which contradicts E ∝ 1/λ.