A long narrow horizontal slit is placed 1 mm above a horizontal p… - Vidyadip

Question

A long narrow horizontal slit is placed $1\ mm$ above a horizontal plane mirror. The interference between the light coming directly from the slit and that after reflection is seen on a screen $1.0m$ away from the slit. Find the fringe$-$width if the light used has a wavelength of $700\ nm$.

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Answer

Given that$, D = 1m, \lambda=700\ \text{nm}=700\times10^{-9}\text{m}$
Since$, a = 2\ mm, d = 2a = 2\ mm = 2 \times 10^{-3}m\ (L$ loyd’s mirror experiment$)$
Fringe width $=\frac{\lambda\text{D}}{\text{d}}=\frac{700\times10^{-9}\text{m}\times1\text{m}}{2\times10^{-3}\text{m}}=0.35\ \text{mm}.$

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