Correct Answer - A::C::D
`(omega_1)/(f_1)+(omega_2)/(f_2)=0`
`:. |omega_1/omega_2|=|(f_1)/(f_2)|`
Let 1-stands for flint glass and 2-stands for crown
glass. Then,
`|(f_1)/(f_2)|=3/2 or |f_1|=1.5|f_2|`
Focal length of flint glass is more. So, its power is
less. Combined focal length (and hence combined power)
is positive. So, convex lens (converging
lens) should be made up of crown glass (having
more positive power).
Now, `1/F=1/(f_1)+1/(f_2)`
`:. 1/150=1/(-1.5f)+1/f`
Solving this equation, we get
`f_2=f=50 cm` and
`f_1=-1.5,f=-75 cm`