When a wave bounces off a surface that it cannot pass through. This does not change the speed or frequency of the wave, but the wave can be flipped upside down.

• A. Diffraction
• B. Wavelength
• C. Amplitude
• D. Reflection

Answer: (D)

Reflection is what happens when a wave meets a boundary it cannot pass through. It bounces back into the original medium, keeping the same speed and frequency because the wave continues in the same medium with the same oscillation rate. The boundary can impose a phase change, and when the boundary acts like a fixed end, the reflected wave inverts, so a crest becomes a trough and the wave appears flipped upside down. The direction follows the rule that the angle of incidence equals the angle of reflection, so the path after bouncing is a mirror of the incoming path.