Find the number of fringes in the interference pattern which is 7.2mm long
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Wavelength of laser light , λ1=640nmλ1=640nm
Fringe width, β1=8.1mmβ1=8.1mm
Wavelength of second light , λ2=?λ2=?
Fringe width, β2=7.2mmβ2=7.2mm
we know that fringe width is given by
β=Dλdβ=Dλd
since D and d are fixed , β∝λβ∝λ
∴β1β2=λ1λ2∴β1β2=λ1λ2
⇒λ2=β2β1×λ1=7.28.1×640=569nm⇒λ2=β2β1×λ1=7.28.1×640=569nm.
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