Question

In Fresnel bi-prism experiment, the distance between the source and the screen $1m$ and that between the source and bi-prism is $10cm$. The wavelength of light used is $6000A^o$. The fringe width obtained is $0.03cm$ and the refracting angle of bi-prism is $1$. The refractive index of the material of bi-prism is

• A. $1.531$
• B. $1.573$
• C. $1.621$
• D. $1.732$

Answer 1

The correct option is B $1.573$

For a fresnel bi-prism, fringe width, $\beta =\frac{D\lambda }{d}$

Hence $d=\frac{D\lambda }{\beta }=2aA(\mu -1)$

Hence, $\mu =1+\frac{D\lambda }{2\beta aA}$

$=\frac{6\times {10}^{-7}}{2\times (3\times {10}^{-4})\times 0.1\times \frac{\pi }{180}}=1.573$