Question

A parallel beam of light of wavelength 5890 A0 is incident on a glass plate having refractive index 𝝁=𝟏.𝟓 such that the angle of refraction in the plate is 600. Calculate the smallest thickness of the glass plate which will appear dark by reflected light.

Answer 1

Given: - λ=5890 x 10^-8 cm

𝜇=1.5

r=60^O

To Find: - t=?
Formula: - 2 𝜇t cos r= n λ

The smallest thickness will be for n=1,

2×1.5×𝑡×cos60=1×5890×10⁻⁸

`t=(5890xx10^-8)/(2xx1.5xx0.5)`
𝒕=𝟑𝟗𝟐𝟔×𝟏𝟎−𝟖𝒄𝒎