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  4. In Fresnel's biprism expt., a mica sheet of refractive index 1.5 and thickness 6 × 10-6 m is placed in the path of one of interfering beams as a result of which the central fringe gets shifted through 5 fringe widths. The wavelength of light used is

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Q. In Fresnel's biprism expt., a mica sheet of refractive index $1.5$ and thickness $6 \times 10^{-6} m$ is placed in the path of one of interfering beams as a result of which the central fringe gets shifted through $5$ fringe widths. The wavelength of light used is

Wave Optics

Solution:

Where $n$ is equivalent number of fringe by which the centre fringe is shifted due to mica sheet
$\lambda=\frac{(\mu-1) t}{n}=\frac{(1.5-1) 6 \times 10^{-6}}{5}=6000 \,\mathring{A}$