If a thin lens is dipped in water, does its focal length change ?

A concave mirror of radius 30 cm is placed in water. It’s focal length in air and water differ by

If a glass prism in dipped in water its dispersive power

The focal length of the lens of refractive index (mu = 1.5) in air is 10 cm. If air is replaced by water of mu = (4)/(3) , its focal length is

A biconvex lens has radius of curvature 20 cm each. If the refractive index of the material of the lens is 1.5, what is its focal length?

A plano-convex lens fits exactly into a plano-concave lens. Their surfaces are parallel to each other if the lenses are made of different materials. Will the combination act as a lens? If so, what is its focal length? Is it convergent or divergent ?

A thin lens of focal length + 12 cm is immersed in water (mu = 1.33). What is its new focal length ?