A solid glass cube is placed at the bottom of a container. When the container is filled with mercury, it is seen that no displacement of the glass cube occurs. Explain why.

When a tiny circular obstacle is placed in the path of light from a distant source,a bright spot is seen at the centre of the shadow of the obstacle. Explain why.

A cylindrical container is to be made from certain solid material which the following constraints : It has a fixed inner volume of V mm^3 , has a 2 mm thick solid wall and is open at the top. The bottom of the container is a solid circular disc of thickness 2 mm and is of radius equal to the outer radius of the container. If the volume of the materia! used to make the container is minimum when the inner radius of the container is 10 mm, then the value of V/(250pi) is

A cylindrical container is to be made from certain solid material with the following constraints : It has a fixed inner volume of V "mm"^(3) , has a 2 mm thick solid wall andis open at the top. The bottom of the container is a solid circular disc of thickness 2 mm and is of radius equal to the outer radius of the container. If the volume of the material used to make the container is minimum when the inner radius of the container is 10 mm, then the value of (V)/(250pi) is-

A transparent cube of glass of refractive index mu and thickness t is placed on a spot of ink drawn on a white paper, When the spot is viewed from above (air) normally, the spot appears to shift through a distance of Delta t towards the observer. What is the value of Delta t ?