If tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, calculate the focal length of objective

Options

A. 100 cm
B. 10 cm
C. 20 cm
D. 25 cm

Answer

A

Explanation

`m = (f_(o))/(f_(e)) = 20 `
and `L = f_(o) + f_(e) = 105 `
`f_(o) + (f_(o))/(20 ) = 105 rArr f_(o) = 100` cm.