What does monochromatic energy mean?

• A. Composed of one wavelength
• B. Contains multiple wavelengths
• C. Energy travels in unison
• D. Wavelength varies with time

Answer: (A)

Monochromatic energy means the energy is carried by waves that have a single fixed wavelength (and thus a single fixed frequency). Since the energy of a photon is E = hf = hc/λ, a single wavelength implies a single photon energy and a very narrow spectral content. That’s why light described as monochromatic is one wavelength rather than a mix of many. The other ideas don’t fit: containing multiple wavelengths would be polychromatic or broadband energy; energy traveling in unison describes phase coherence rather than the number of wavelengths; and a wavelength that varies with time would be a changing frequency or chirped signal, not monochromatic light.