A slanted beam changes speed and direction when it crosses between air and water.
The dashed “normal” points straight out from the surface. Tap to compare a straight ray with a slanted one.
Change the ray’s angle from the dashed normal. Into water it bends toward that line; out to air it bends away.
Two rays arrive from an unseen source. Tap trace to extend their directions straight backward. Their crossing is where a viewer would place the source.
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
