Question

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}} $

Answer 1

Answer: (C)

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 $