List of top Physics Questions on Ray optics and optical instruments asked in UP CPMT

Diameter of aperture of a plano-convex lens is $6\, cm$ and thickness at the centre is $3\, mm$. If the speed of light in the material of the lens is $2 \times 10^8 \,m \,s ^{-1}$, the focal length of the lens is

The focal length of the field lens (which is an achromatic combination of two lenses) of a telescope is $90$ cm. The dispersive powers of the two lenses in the combination are $0.024$ and $0.036$.The focal lengths of the two lenses are