Ray Optics and Optical Instruments

A double convex lens made of glass of refractive index 1.5 and radii of curvature of the curved surfaces 20 cm each is immersed in a liquid of refractive index nL. The correct plot showing the variation of the power, in the units of diopter (D), as a function of nL is:

1. [figure]
2. [figure]
3. [figure]
4. [figure]

A beam of polychromatic light passes through a thin prism of prism angle 6 . The refractive index of the material of the prism varies with wavelength ( ) as n( )= + 2, where =3 m-1 and =0.096 m2. If is the wavelength at which the angle of minimum deviation Dm is smallest, then the correct value of Dm at is

1. 6.4
2. 4.8
3. 3.2
4. 2.4