A cubical vessel with non-transparent walls is so located that the eye of an observer does not see its bottom but sees all of the wall CD.
To what height should water be poured into the vessel for the observer to see an object F arranged at a distance of `b=10 cm` from corner D? The face of the vessel is `a=40 cm.` Refractive index of water is `4/3.`

Answer

B, C

Explanation

Since, the vessel is cubical, `angleGDE=45^@`
and `GE=ED=h(say)`
then `EF=ED-FD=(h-10)`
Further, `4/3=(sin45^@)/sinr`
`:. r=32^@`

Now, `(EF)/(GE)=tan r=tan 32^@`
`:. (h-10)/h=0.62`
Solving this, we get
`h=26.65 cm`