question_answer

If the wavelength of incident light on a (i) concave mirror, and (ii) convex lens is increased, how will the focal length of each of these change?              

Answer:

                (i) Focal length of the concave mirror remains unchanged. (ii) As \[f=\frac{1}{\mu -1}\] For \[{{\lambda }_{2}}>{{\lambda }_{1}},\]           \[{{\mu }_{2}}<{{\mu }_{1}},\]    \[\therefore \]                \[{{f}_{2}}>{{f}_{1}}\] i.e., when wavelength of incident light is increased, focal length of the convex lens increases.