How does the energy of light relate to its wavelength?

• A. Light of shorter wavelengths has higher energy than light of longer wavelengths.
• B. Light of shorter wavelengths has lower energy than light of longer wavelengths.
• C. Energy is independent of wavelength.
• D. Energy only depends on intensity, not wavelength.

Answer: (A)

Light energy is carried by photons, and each photon’s energy is proportional to its frequency (or inversely proportional to its wavelength). Since E = h f and f = c/λ, we get E = h c / λ. So shorter wavelengths have higher energy per photon. For example, blue light (450 nm) delivers more energy per photon than red light (700 nm). Remember, the beam’s total energy also depends on how many photons are present (the intensity), not just the energy per photon.