A monochromatic ray of light travels through glass slab and water column. The number of waves in glass slab of thickness $$4 \mathrm{~cm}$$ is the same as in water column of height $$5 \mathrm{~cm}$$. If refractive index of glass is $$\frac{5}{3}$$ then refractive index of water is

The radii of curvature of both the surfaces of a convex lens of focal length '$$\mathrm{f}$$' and focal power '$$\mathrm{P}$$' are equal. One of the surfaces is made plane by grinding. The new focal length and focal power of the lens is respectively

A glass slab has refractive index '$$\mu$$' with respect to air and the critical angle for a ray of light in going from glass to glass to air is '$$\theta$$' If a ray of light is incident from air on the glass with angle of incidence '$$\theta$$', then the corresponding angle of refraction is

'Circle of least confusion' refers to which one of the following defects occurring in images formed by mirrors or lenses?