The intensity of the portion of the incident beam that continues forward in the same general direction that it was traveling is the _______.

• A. Transmitted intensity
• B. Incident intensity
• C. Reflected intensity
• D. IRC

Answer: (A)

When a beam meets a boundary between two media, energy can either bounce back (reflected) or pass into the second medium (transmitted). The portion that continues forward in the same general direction into the second medium is the transmitted intensity. It represents the energy flux that makes it through the boundary; the incident intensity is the energy before hitting the boundary, and the reflected intensity is the energy that returns toward the source. If there’s no absorption, transmitted plus reflected (plus any absorbed portion) accounts for the total incident energy. In many contexts, the transmitted part is what you’re looking for when you ask about energy continuing forward.