question_answer

In Ramsdens eye piece the field lens and eye lens have focal lengths f1 and f2 respectively and separated by a distance d, then:

A)  \[{{f}_{1}}={{f}_{2}}\frac{2}{3},d=\frac{2}{3}{{f}_{1}}\] 

B)  \[{{f}_{1}}={{f}_{2}},d={{f}_{1}}+{{f}_{2}}\]

C)  \[{{f}_{1}}={{f}_{2}},d=\frac{2}{3}f\]

D)  \[{{f}_{1}}=3{{f}_{2}},d={{f}_{1}}+{{f}_{2}}\]

Correct Answer: C

Solution :

                 It consists of two coaxial plano-convex lenses of equal focal lengths\[{{f}_{1}}\] and \[{{f}_{2}}\] separated by a distance \[\frac{2}{3}f.\] It means, \[{{f}_{1}}={{f}_{2}}\]and \[d=\frac{2}{3}f\]