NEET-XII-Physics
17: Light Waves
- #22A long narrow horizontal slit is paced 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⋅0 m away from the slit. Find the fringe-width if the light used has a wavelength of 700 nm.Ans : Given:
Separation between two slits, `` d\text{'}=2d=2\,\mathrm{\,mm\,}=2\times {10}^{-3}\,\mathrm{\,m\,}`` (as d = 1 mm)
Wavelength of the light used, `` \lambda =700\,\mathrm{\,nm\,}=700\times {10}^{-3}\,\mathrm{\,m\,}``
`` ``
Distance between the screen and slit (D) = 1.0 m
It is a case of Lloyd's mirror experiment.
`` \,\mathrm{\,Fringe\,}\,\mathrm{\,width\,},\beta =\frac{\,\mathrm{\,\lambda D\,}}{d\text{'}}``
`` =\frac{700\times {10}^{-9}\times 1}{2\times {10}^{-3}}``
`` =0.35\times {10}^{-3}\,\mathrm{\,m\,}=0.35\,\mathrm{\,mm\,}``
Hence, the width of the fringe is 0.35 mm.
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