Correct Answer - A::B::C::D
Given that:
`f_1=` focal length of converging lens =30 cm`
f_2=` focal length of diverging lens =20 cm
and d= distance between them =15 cm
Let, F=equivalent focal length
so, `1/F=1/f_1+1/f_2-d/(f_1f_2)`
`=1/30+(1/50)-(5/(30(-20)))`
`=1/1.20`
`rarr F=120cm
rarrThe equivalent lens is a converging one. Distance from diverging lens so that emergent beam is parallel (image at infinity)
`d_1=(dF)/f_1=(15xx120)/30=60cm`
It should be placed 60 cm left to diverging lens. Object should be placed ltbr. `(120-60)=60cm`
from diverging length
similarly `d_2=(dF)/2=(15xx120)/20`
`=90 cm `
`so it should be placed (120+90)lcm`
`=210 cm right to converging lens.