In a laboratory four convex lenses `L_(1), L_(2), L_(3)` and `L_(4)` of focal lengths `2,4,6` and `8 cm` respectively are available. Two of these lenses form a telescope of length `10 cm` and magnifying power 4 . The objective and eye lenses are

Options

A. `L_(2),L_(3)`
B. `L_(1),L_(4)`
C. `L_(1),L_(2)`
D. `L_(4),L_(1)`

Answer

4

Explanation

Length of tube = 10 cm
`f_(0)+f_(e)=10cm`
magnification , m = `f_(0)/f_(e) = 4`
`f_(0)=4f_(e)`
`:. 5f_(e)=10`
`f_(e)`=2cm and `f_(0)` = 8cm