Question

A cubical vessel with opaque walls, is so placed that the eye of an observer cannot see its bottom but can see the entire wall CD. A small object is placed at O at a distance b = 10 cm from corner D. What minimum depth of water $(\mu =\frac{4}{3})$ should be poured into the vessel which will enable the observer to see the object?

• A. 16.7 cm
• B. 26.7 cm
• C. 36.7 cm
• D. 46.7 cm

Answer 1

The correct option is B 26.7 cm

Incident angle is $tani=\frac{l}{l}=1$,

$⟹i={45}^o$

Let L be length.

Let the water be filler up to h height.

By Snell's law ${\mu }_{1}sini={\mu }_{2}sinr$

$sin45=\frac{4}{3}sinr$

$r={32}^o$

Now due to h height of water the refraction is shifted by 10 cm . So $b=h(tan45-tan32)=10cm$

$10cm-h(1-0.63)$

$h=26.7cm$