Question

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

Answer 1

Please mention in diagram where is A , B , C and D