Which term describes the fraction of incident energy that is reflected at a boundary?

• A. Intensity Transmission Coefficient
• B. Intensity Reflection Coefficient
• C. Impedance Ratio
• D. Attenuation Coefficient

Answer: (B)

When a wave reaches a boundary between two media, part of the energy bounces back into the first medium. The quantity that captures exactly how much energy is reflected is the intensity reflection coefficient. For plane waves at normal incidence, it can be expressed in terms of the two media’ impedances Z1 and Z2 as R = |(Z2 − Z1)/(Z2 + Z1)|^2. This fraction, which ranges from 0 to 1, represents the portion of incident energy that is reflected, while the rest is transmitted.

If the impedances match, there is no reflection and all energy is transmitted. If the impedances are very different, most of the energy reflects. The other terms don’t describe the reflected energy fraction: the transmission coefficient describes the transmitted energy, the impedance ratio just compares the impedances without giving the energy fraction, and the attenuation coefficient describes how energy decreases as it travels through a medium, not at the boundary.