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

D

Explanation

`L=f_(0)+f_(e)=10,M=(f_(0))/(f_(e))=4` ,` :.f_(0)=4f_(e)`
`L=4f_(e)+f_(e)=10`,
`f_(e)=(10)/(5)=2` cm, `f_(0)=4xx2=8` cm
`:.` The objective lens is `L_(4)` and eye lens is `L_(1)`.