A slanted beam changes speed and direction when it crosses between air and water.
Tap the beam. A straight ray follows the dashed normal; a slanted ray bends exactly where it crosses the surface.
Change the ray’s angle from the dashed normal. Into water it bends toward that line; out to air it bends away.
Two solid bent rays reach the eye. Tap trace: follow each arriving direction backward in a straight dashed line. Their crossing is the apparent light spot.
A real coin at the bottom sends two solid rays that bend at the surface and reach one eye. No dashed traces or image coin yet.
A coin rests on the bottom. Your eye looks from air above.
Where will the coin appear?
Choose, then trace both rays backward until their dashed extensions meet.
experiment ready
