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Question

Why does a water tank filled with water appear shallower when viewed from the top?

This question was previously asked in
SSC CGL 2017 (Tier 1) Previous Year Paper (16-Aug-2017) (Shift 1)
The correct answer is

Due to refraction

Light rays from the bottom of the tank travel from water (optically denser) to air (rarer), and on crossing the interface they bend away from the normal. The eye traces these refracted rays back in straight lines, locating the bottom at a virtual image closer to the surface.

The relation is \(\mu = \dfrac{\text{real depth}}{\text{apparent depth}}\); since \(\mu_{water} \approx 1.33 > 1\), the apparent depth is less than the real depth. This effect is refraction — not reflection, diffraction, or total internal reflection.

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