Question

A plano-convex glass lens of radius of curvature 1.8 m rests on an optically flat glass plate. The arrangement is illuminated from above with monochromatic light of 559-nm wavelength. The indexes of refraction of the lens and plate are 1.6. Determine the radii of the first and second bright fringes in the reflected light.

Answer 1

Answer:

0.000709 m

0.00122 m

Explanation:

R = Radius of curvature = 1.8 m

λ =  Wavelength = 559 nm = 559×10⁻⁹ m

Radius of bright fringe

$r=\sqrt{(m+0.5)\lambda R}$

First bright fringe means at m = 0

$r=\sqrt{(0+0.5)559\times 10^{-9}\times 1.8}=0.000709\ m$

First second fringe means at m = 1

$r=\sqrt{(1+0.5)559\times 10^{-9}\times 1.8}=0.00122\ m$

∴ Radius of the first bright fringe is 0.000709 m

∴ Radius of the second bright fringe is 0.00122 m