Define the principal axis of a lens.

An equiconvex lens with radii of curvature of magnitude R each,is put over a liquid layer poured on top of a plane mirror.A small needle ,with its tip on the principal axis of the lens,is moved along the axis until its inverted real image coincides with the needle itself.The distance of the needle from the lens is measured to be a as shown in Fig.2.53. On removing the liquid layer and repeating the ezperiment,the distance is found to be b as shown in Fig.254 .Gien that tow values of distances meeawured reepresent the focal length values in the two cases, obtain a formula for the refractive index of the liquid. .

Define the principal focus of concave mirror.

Define principle axis of a spherical mirror.

The figure TBQ 9.38 shows an equiconvex lens (of refractive index 1.50) in contact with a liquid layer on top of a plane mirror. A small needle with its tip on the principal axis is moved along the axis until its inverted images if found at the positions of hte needle. The distance of the needle from the lens is measured to be 45.0 cm. The new distane is measured to be 30.0 cm. What is the refractive index of the liquid?