The position of fical image formed by the given lens combination from the third lens will be at a distance of `f_1=+10cm,f_2=-10cm,f_3=+30`

Options

A. 15 cm
B. Infinity
C. 45 cm
D. 30 cm

Answer

D

Explanation

For `1^(st) `lens -
`f_(1) = 10 cm , " " u_(1) = - 30 `cm
`(1)/(v_(1)) = (1)/(10) - (1)/(30) rArr v_(1) = 15 `cm
For `2^(nd)` lens-
`u_(2) = 15 - 5 = 10 cm, f_(2) = -10` cm
`therefore (1)/(v_(2)) = 0 rArr v_(2) = infty`
For `3^(rd)` lens-
`u_(3) = infty, f_(3) = 30 ` cm
`(1)/(u_(3)) = (1)/(f_(3)) rArr u_(3) = f_(3) = 30 ` cm .