Final answer:
The phenomenon of concentric circular ripples formed when a water drop hits a lake is called diffraction, which occurs when waves spread out after encountering an obstacle or passing through an opening.
Step-by-step explanation:
When a drop of water hits the surface of a lake and forms concentric circular ripples, the phenomenon is called diffraction. Diffraction occurs when a wave encounters an obstacle or a slit that is comparable in size to its wavelength, causing the waves to spread out as they pass through an opening or around an edge. An example of this can be seen with water waves, such as those generated by a drop of water falling onto a smooth water surface, which then travel outward in a circular pattern.
In context with other wave interactions, reflection occurs when a wave bounces off a surface, refraction is the bending of waves as they pass from one medium to another, and interference is the phenomenon where waves overlap and combine to form a new wave pattern, as seen in Figure 3.16 where waves reflect from rocks and create complex patterns on the water’s surface.