A swimming pool always looks shallower than it really is — why, and by how much?
Light from the bottom bends away from the normal as it leaves the water, so your eye sees the bottom raised.
Light from the bottom bends away from the normal as it leaves the water, so your eye sees the bottom raised. The apparent depth = real depth / n. For water n ≈ 1.33, so a 4 m pool looks only about 3 m deep. That's exactly why stepping into 'shallow-looking' water can be a nasty surprise.
Key point
apparent depth = real depth / n (≈ 3/4 of the true depth for water).
Common mistake
assuming you see the true depth straight down.
Memory tip
divide the real depth by the refractive index to get what you see.
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