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

Question

A long narrow horizontal slit is placed 1mm 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 700nm.

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Answer

Given that, D = 1m, $\lambda=700\text{nm}=700\times10^{-9}\text{m}$
Since, $a = 2mm, d = 2a = 2mm = 2 × 10^{-3}m$ (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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