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. `46.0 cm`
B. `50 cm`
C. `54.0 cm`
D. `37.3 cm`

Answer

C

Explanation

Here, `f_(0) = 40 cm, f_(e) = 4 cm, u_(0) = - 200 cm`
As `(1)/(v_(0)) - (1)/(u_(0)) = (1)/(f_(0))`
`:. (1)/(v_(0)) = (1)/(f_(0)) + (1)/(u_(0))`
`= (1)/(40) - (1)/(200) = (4)/(200) = (1)/(50)`
In normal adjustment, distance between objetive and eye piece `= v_(0) + f_(e) = 50 + 4 = 54 cm`