Here a thin film is formed between curve surface of cylinder and flat surface of glass which results in interference pattern. For a fringe, locus and all point having equal thickness will be straight line parallel to length of the piece. At line of contact, for first reflection, as ray passes from glass to air, no phase changes and as it goes from air to glass, it will change phase. So, both rays will be out of phase resulting in dark fringe.



as ${\text{t}}_{\text{n}+1}-{\text{t}}_{\text{n}}=\frac{\lambda }{2\mu }=\text{costant}$

$\text{w}=\frac{{\text{t}}_{\text{n}+1}-{\text{t}}_{\text{n}}}{\theta }$

As we go outward, $\theta$ increases

w decreases. So, $3\mathrm{rd}$ option is wrong.