Force on Strip in YDSE!

Figure shows two identical narrow slits $$S_1$$ and $$S_2$$.

A very small completely absorbing strip is placed at distance '$$y$$' from the point $$C$$.

'$$C$$' is the point on the screen equidistant from $$S_1$$ and $$S_2$$.

Assume ($$\lambda << d << D$$) where $$\lambda, d$$ and $$D$$ have usual meaning.

When $$S_2$$ is covered, the force due to light acting on strip is '$$F$$' and when both slits are opened the force acting on strip is $$2F$$. Minimum positive '$$y$$' ($$<<D$$) coordinate of the strip in terms of $$\lambda, d$$ and $$D$$ is $$\frac{\lambda D}{2md}$$.

What is the value of $$m$$?

×