A thin converging lens of focal length f is placed bewteen an obejct an a screen at a distance D apart, (displacement method)

Options

A. if `Dgt4f`, there are two positions of the lens as which a sharp image of the object is formed on the screen
B. `f=(D^2-x^2)/(4D),x`, distance between two position of the lens
C. `m_1=(D+x)/(D-x)`,`m_2=(D-x)/(D+x)`, for two positions of the lens Object size `O=sqrt(I_1I_2)`,`f=(x)/(m_1-m_2)`
D. all options are correct.

Answer

A