Which Equation Expresses The Energy Of A Photon In Terms Of Wavelength?

Which Equation Expresses The Energy Of A Photon In Terms Of Wavelength?

• A. E = hf
• B. E = h c / λ
• C. E = λ / (h c)
• D. E = c / (h λ)

Answer: (B)

This question tests how photon energy depends on wavelength. A photon’s energy is E = h f, where h is Planck’s constant and f is the frequency. Light has a fixed speed c, and frequency and wavelength are linked by f = c / λ. Substituting f into the energy expression gives E = h (c / λ) = h c / λ. So the energy expressed in terms of wavelength is E = h c / λ, which correctly shows energy decreasing as wavelength increases and uses the correct combination of constants to yield energy in joules. The other forms don’t fit: E = h f is in terms of frequency, not wavelength; and E = λ / (h c) or E = c / (h λ) place λ in the wrong position and don’t produce the correct units or dependence on wavelength.

This question tests how photon energy depends on wavelength. A photon’s energy is E = h f, where h is Planck’s constant and f is the frequency. Light has a fixed speed c, and frequency and wavelength are linked by f = c / λ. Substituting f into the energy expression gives E = h (c / λ) = h c / λ. So the energy expressed in terms of wavelength is E = h c / λ, which correctly shows energy decreasing as wavelength increases and uses the correct combination of constants to yield energy in joules.

The other forms don’t fit: E = h f is in terms of frequency, not wavelength; and E = λ / (h c) or E = c / (h λ) place λ in the wrong position and don’t produce the correct units or dependence on wavelength.