Apparent depth
Intermediate
Objects in water look shallower.
d' = d/nAn object under water seems shallower: apparent depth = real depth/n (viewed from above). A pool of depth 2 m appears 1.5 m deep.
Spearfishers aim lower.
The formula holds for near-normal viewing.
In more detail
Objects in water appear shallower than they are, because light from them is refracted away from the normal as it leaves the water. Apparent depth equals real depth divided by refractive index.
Real-world uses
- Swimming pool depths look shallower than they are.
- Fishing spears must be aimed below the apparent position of a fish.
- A fish in a pond appears closer to the surface than it really is, which is why spearfishers aim lower.
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Frequently asked questions
Why does the fish appear higher?
Because the refracted rays seem to come from a point closer to the surface.
Does the same work from above?
Yes, viewed from above, objects in water appear shallower.
Is the apparent depth always shallower?
When viewed from above, yes. The apparent depth is the real depth divided by the refractive index of the water.
Related topics in Optics
Refraction of light · Refractive index · Snell's law · Critical angle · Total internal reflection · Applications of TIR