Shallow Lies
Bent sticks, lifted coins — refraction's illusions
What this lesson covers
Why it matters
Every pond you have ever seen is lying about its depth. Fishermen, herons and physicists all know: the fish is deeper than it looks.
The idea in plain words
The illusion, explained. Tap the exhibits.
apparent depth < real depth
Why must a heron strike BELOW where the fish appears?
Aim under the illusion — evolution taught herons Snell's law
- exhibit 1: bent stick — the underwater half's image is lifted → the stick seems kinked at the surface
- exhibit 2: raised coin — pools look shallower than they are — a real swimming-safety fact
- the vocabulary: real vs virtual — real images can fall on a screen; virtual ones (like the raised coin) exist only for your eye
- The fish's image is raised by refraction
- The real fish is deeper than the image
Predict first
A coin at the bottom of a bucket of water appears…
Light from the coin bends AWAY from the normal on leaving the water; your eye traces the bent rays back to a raised virtual coin.
- raised — shallower than it really is — correct
- deeper than it is
- exactly where it is
What you do
Slide the depth and swap the liquid — watch the ghost coin float above the real one.
Check yourself
A pencil half in water looks bent because…
Take it out — straight as ever. The kink lives in the light, not the pencil.
A virtual image is one that…
You see it clearly — but no light actually meets there, so a screen shows nothing.
Ponds are dangerous to non-swimmers partly because refraction makes them look…
The 'knee-deep' pond may be chest-deep — physics' most practical safety warning.
- light from the underwater part refracts at the surface — correct
- water softens wood
- the glass distorts it
- cannot be caught on a screen — correct
- doesn't exist
- is always magnified
- shallower than they are — correct
- deeper than they are
- narrower