A telescope has an objective of focal length $$60 \mathrm{~cm}$$ and eyepiece of focal length $$5 \mathrm{~cm}$$. The telescope is focussed for least distance of distinct vision $$300 \mathrm{~cm}$$ away from the object. The magnification produced by the telescope at least distance of distinct vision is

Figure below shows a lens of refractive index, $$\mu=1.4$$. $$C_1$$ and $$C_2$$ are the centres of curvature of the two faces of the lens of radii of curvature $$4 \mathrm{~cm}$$ and $$8 \mathrm{~cm}$$ respectively.

The lens behaves as a

When a biconvex lens of glass of refractive index 1.5 is dipped in a liquid, it acts like a plane sheet of paper. This means the refractive index of the liquid is