Numerical

A wedge shaped air film having angle 40 seconds is illuminated by monochromatic light. Fringes are observed vertically through a microscope. The distance between 10 consecutive dark fringes is 1.2 cm. find the wavelength of monochromatic light used.

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#### Solution

Given:

Θ = 40 seconds = `40 / 3600` degrees

`= 40 / 3600 xx ᴨ / 180 "radians," β = 0.12 cm`

Formula:

Spacing between the consecutive bright fringes is, β = `λ / (2θ)` (for air film)

The wavelength is, λ = 2β × θ

`Λ = 2 xx 0.12 xx 40 xx ᴨ / 3600 xx 180`

`= 46.54 xx 10^-8 cm`

`λ = 4654 A^0 `

Concept: Wedge Shaped Film(Angle of Wedge and Thickness Measurement)

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