Question

In bi-prism experiment when the slit and the eyepiece are set at $1cm$ and $100cm$, the width of $10$fringes is found to be $9.72mm$. If the distance between the images formed in the eyepiece in two positions of the lens is $0.3mm$ and $1.2mm$ respectively ,then the wavelength of light used is

• A. $5832A^o$
• B. $5840A^o$
• C. $5820A^o$
• D. $5700A^o$

Answer 1

The correct option is A $5832A^o$

Here $d=\sqrt{d_1{d}_2}$

$=\sqrt{\left(0.3\right)\left(1.2\right)}mm=0.6mm$

Width of ten fringes $=9.72$ mm

Hence width of each fringe$=0.972$ mm$=\frac{D\lambda }{d}$

Hence $\lambda =\frac{d\left(0.972\right)}{D}mm=5832A^{\circ }$