Question

A glass wedge of angle $0.01$ radian and $\mu=1.5$ is illuminated by monochromatic light of wavelength $6000\,\mathring{A}$ falling normally on it. At what distance from wedge will $10^{\text {th }}$ dark fringe be observed by reflected light?

• A. 0.1 mm
• B. 0.2 mm
• C. 0.3 mm
• D. 0.4 mm

Answer 1

Answer: (B)

For dark fringe, $2 \mu t=n \lambda$
$t=\frac{n \lambda}{2 \mu}=\frac{(10)\left(6000 \times 10^{-10} m \right)}{2(1.5)}$
$=2 \times 10^{-6}\, m$
$x=\frac{t}{\theta}=\frac{\left(2 \times 10^{-6} m \right)}{(0.01\, rad )}$
$=2 \times 10^{-4} m =0.2\, mm$