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

4

Explanation

For 1 st lens, `u_(1)=-30,f_(1)=+10,`
Formal of lens `=(1)/(v_(1))-(1)/(u_(1))=(1)/(f_(1))`
`therefore(1)/((v_(1)))+(1)/(10)=(1)/(10)`
or `v_(1)=1` om at `I_(1)` behind the lens. The imgage `I_(1)` serves as virtual object for concave lens. For second lens, which is concave,
`u_(2)=(15-5)=10cm.`
Image distance from third lens `f_(3)=30 cm.`