1.

A cubical vessel with non - transparent walls is so located that eye E of observer cannot see its bottom but can see all of the wall CD. To what height should water be filled in vessel for the observer to see an object O placed at a distance b = 10 cm from the corner C(.^(a)mu_(omega)=(4)/(3))

Answer»

16.5 cm
20.4 cm
26.7 cm
28.2 cm

Solution :( c) As vessel is cubical
`angle ACB =45^(@)`
Let h be the required height
NO =h - b = h tan r


or `h = (b)/(1 - tan r)`
Now `mu = (SIN 45)/(sin r)`
`sin r = (1)/(sqrt(2)r) "" therefore COS r = sqrt(1 - sin^(2) r)`
so `h=(b)/(1-(1)/(sqrt(2MU^(2)-1)))=(bsqrt(2mu^(2)-1))/(sqrt(2mu^(2)-1-1))`
`therefore h = 26.7 cm`


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