Final answer:
Reflection is the change in direction of a wave when it strikes a barrier and bounces off of it. It applies to both mechanical and electromagnetic waves, with phenomena such as echoes and visible images in a mirror being common examples. In certain conditions, waves can invert upon reflection.
Step-by-step explanation:
Reflection is the change in direction of a wave when it bounces off a barrier. This is typically observed when waves, such as sound waves or light waves, encounter obstacles or media transitions and are reflected back rather than being absorbed or transmitted through. The most accurate description of reflection is the change in direction of a wave after hitting a boundary. This can sometimes involve an inversion, which means a wave can flip vertically upon reflection if it encounters a fixed end, causing a crest to become a trough and vice versa.
For example, when you shout toward a cliff, the sound waves reflect off the rigid surface and return as an echo. Electromagnetic waves, like light, similarly reflect off surfaces such as mirrors, allowing us to see ourselves. The reflection spectrum describes the behavior of incident waves when interacting with a substance - whether they're reflected, absorbed, or transmitted.
When mechanical waves encounter the end of their medium that leads to a vacuum, they reflect backward since they require a medium to propagate. Electromagnetic waves, on the other hand, can continue into the vacuum as they do not rely on a medium.