A broad source of light of wavelength 680 nm illuminates normally two glass plates 120 m long that meet at one end and are seperated by a wire 0.048 mm in diameter at the other end. Find the number of bright fringes formed over the 120 mm distance.
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Fringe Width β in case of variable thickness wedge shaped film is :
β=λ/2μθ
See the attachment.
From the figure we get Tanθ=θ=y/l ---------(1)
Let N be the number of fringes formed over length l
l=Nβ
l=N(λ/2μθ)
N=2μlθ/λ
N=2uy/λ [∵ θ=y/l]
N=2x1x0.048x 10⁻³ /680 x 10 ⁹
N=0.096x 10⁻³ /680 x 10 ⁹
N=141
β=λ/2μθ
See the attachment.
From the figure we get Tanθ=θ=y/l ---------(1)
Let N be the number of fringes formed over length l
l=Nβ
l=N(λ/2μθ)
N=2μlθ/λ
N=2uy/λ [∵ θ=y/l]
N=2x1x0.048x 10⁻³ /680 x 10 ⁹
N=0.096x 10⁻³ /680 x 10 ⁹
N=141
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