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

Options

A. `37.3cm`
B. `46 .0cm`
C. `50.0cm`
D. `54.0cm`

Answer

D

Explanation

Using lens formula for objective lens
`( 1)/(v_(o))-(1)/(u_(o))=(1)/(f_(o))implies ( 1)/(v_(o))=(1)/(f_(o))+(1)/(u_(o))`
`implies(1)/(v)=(1)/(40)+(1)/(-200)=(+5-1)/(200)`
`impliesv_(o)=50cm`
Tube length`1=|v_(o)|+f_(o)=50+4=54cm`