Optics Question 849

Question: In Fresnel’s biprism experiment the width of 10 fringes is 2cm which are formed at a distance of 2 meter from the slit. If the wavelength of light is $ 5100\overset{o}{\mathop{A}} $ then the distance between two coherent sources will be

Options:

A) $ 5.1\times {{10}^{-4}}m $

B) $ 5.1\times 10^{4}m $

C) $ 5.1\times {{10}^{-4}}mm $

D) $ 10.1\times {{10}^{-4}}cm $

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Answer:

Correct Answer: A

Solution:

[a] $ d=\frac{D\lambda }{\beta } $ …(i)

According to question, $ \lambda =5100\times {{10}^{-10}}m $

$ \beta =\frac{2}{10}\times {{10}^{-2}}m $ …(ii) D=2m, d=?

From eqs. (i) and (ii) $ d=\frac{2\times 51\times {{10}^{-8}}}{2\times {{10}^{-3}}}=5.1\times {{10}^{-4}}m $



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