Wavelength of light used in an optical instruments are $\lambda_1=4000 \mathop {\rm{A}}\limits^{\rm{o}}$ and $\lambda_2=5000 \mathop {\rm{A}}\limits^{\rm{o}}$, then the ratio of their respective resolving powers (corresponding to $\lambda_1$ and $\lambda_2$ ) is

What minimum separation between two objects a human eye would be able to resolve, if the eye pupil diameter is 2 mm and the two objects are 20 m away from the eye?

(Assume, human eye to be equivalent to a convex lens and consider the average wave length of light as 600 nm )

The shape of wavefront of light diverging from point source

The limit of resolution of a telescope is $3.0 \times 10^{-7} \mathrm{rad}$. Assuming that it is used to see the light of wavelength 525 nm from a star, what should be the diameter of the objective?