Question

Figure shows a modified Fresnel biprism experiment with monochromatic source of wavelength $500nm$. The refracting angle of glass prism is $2^o$. Find the fringe width.

• A. $0.1125mm$
• B. $0.125mm$
• C. $0.15mm$
• D. $0.3mm$

Answer 1

Answer: (A)

$0.1125mm$

Refractive index of glass ,${\mu }_g=1.5$

Given: $a=.575mD=a+b=1.5m{\lambda }_o=500nm\delta =2^o$

$d=2a({\mu }_g-\mu )\delta$

$\beta =\frac{{\lambda }_{o}D}{d}=\frac{{\lambda }_{o}D}{2a({\mu }_g-\mu )\delta }$

$\beta =\frac{500\times {10}^{-9}\times 1.5}{2\left(.575\right)(1.5-\frac{4}{3})\times 2\times \frac{\pi }{180}}$

$\beta =.1125mm$