Which is a correct statement about energy at the boundary?

Which is a correct statement about energy at the boundary?

• A. The sum of reflected and transmitted intensities is less than the incident intensity.
• B. The sum of reflected and transmitted intensities equals the incident intensity.
• C. The transmitted intensity is greater than the incident intensity.
• D. The reflected intensity is greater than the transmitted intensity.

Answer: (B)

When a wave encounters a boundary between two non-absorbing media, the energy carried by the incoming wave is split into a reflected portion and a transmitted portion. Energy conservation requires that all the energy going toward the boundary is accounted for by these two portions, with none lost to absorption. Therefore, the intensity of the reflected wave plus the intensity of the transmitted wave equals the intensity of the incident wave. If the second medium were lossy, some energy would be converted to heat or other forms, and the sum would be less than the incident intensity. This is why the statement that the sum of reflected and transmitted intensities equals the incident intensity is the correct description.

When a wave encounters a boundary between two non-absorbing media, the energy carried by the incoming wave is split into a reflected portion and a transmitted portion. Energy conservation requires that all the energy going toward the boundary is accounted for by these two portions, with none lost to absorption. Therefore, the intensity of the reflected wave plus the intensity of the transmitted wave equals the intensity of the incident wave. If the second medium were lossy, some energy would be converted to heat or other forms, and the sum would be less than the incident intensity. This is why the statement that the sum of reflected and transmitted intensities equals the incident intensity is the correct description.