If in a Young's double slit experiment the slit separation is doubled and the distance of the screen from the slits is reduced to half, then the fringe widths become how many times their original value?

Which of the following phenomena produces the colour in soap bubble?

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 )