A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To

Question

A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance\

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(b) : Here $f_{o}=40 \mathrm{~cm}, f_{e}=4 \mathrm{~cm}$ Tube length $(l)=$ Distance between lenses $$ =v_{o}+f_{e} $$ For objective lens, $$ u_{o}=-200 \mathrm{~cm}, v_{o}=	ext { ? } $$ $$ \frac{1}{v_{0}}-\frac{1}{u_{0}}=\frac{1}{f_{0}} 	ext { or } \frac{1}{v_{0}}-\frac{1}{-200}=\frac{1}{40} $$ or $\frac{1}{v_{0}}=\frac{1}{40}-\frac{1}{200}=\frac{4}{200} \quad 	herefore \quad v_{0}=50 \mathrm{~cm}$\ $	herefore \quad l=50+4=54 \mathrm{~cm}$\