The critical angle of a medium having the refractive index $$\sqrt2$$ is :

When angle of incidence on one face of the equilateral glass prism is $$3 / 4^{\text {th }}$$ of the angle of prism, the ray of light undergoes minimum deviation. If the velocity of light in vacuum is '$$c$$' then the velocity of light in the glass is :

A person has a normal near point $$25 \mathrm{~cm}$$. What is the magnifying power of the simple microscope he used, if the focal length of the convex lens used is $$10 \mathrm{~cm}$$ and the final image is formed at the least distance of distinct vision?

A lens of power $$+1 \mathrm{D}$$ is made in contact with another lens of power $$-2 \mathrm{D}$$ the combination will then act as a: