Question

Observation of a slip gauge of flatness interferometer produced fringe counts numbering 10 and 14 for two readings. The second reading is taken by rotating the setup by ${180}^{\circ }$. Assume that both faces of the slip gauge are flat and the wavelength of the radiation is $0.5086\mu$m. The parallelism error (in $\mu m)$ between the two faces of the slip gauge is

• A. $0.2543$
• B. $1.172$
• C. $0.5086$
• D. $0.800$

Answer 1

The correct option is C $0.5086$

$\text{Parallelism error}$

$=\left(\frac{n_2-n_1}{2}\right)\times \frac{\lambda }{2}=\left(\frac{14-10}{2}\right)\times \frac{0.5086}{2}$

= $0.5086\mu m$