In Fresnel's biprism expt., a mica sheet of refractive index 1.5 and thickness 6 × 10−6m 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
A
6000 oA
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B
8000 oA
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C
4000 oA
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D
2000 oA
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Solution
The correct option is C 6000 oA Where n is equivalent number of fringe by which the centre fringe is shifted due to mica sheet λ=(μ−1)tn=(1.5−1)6×10−65=6×10−7m=6000oA