Define resolving power of microscope. Write its formula. How will it vary, when
(a) wavelength of incident light is decreased?
(b) aperture of the objective lens is decreased?

The resolving power is the inverse of the distance between two objects that can be just resolved.

It is given by Abbe's criterion

Resolving power $=\frac{1}{\Delta d}=\frac{2a}{\lambda }$

where $a$ is the numerical aperture

$\lambda$ is the wavelength of the objective lens used

(a) When wavelength of incident light is decreased, the resolving power increases.

(b) When aperture of the objective lens is decreased, the resolving power decreases.