In two separate setups for Biprism experiment using same wavelength, fringes of equal width are obtained. If…
In two separate setups for Biprism experiment using same wavelength, fringes of equal width are obtained. If ratio of slit separation is $2: 3$ then the ratio of the distance between the slit and screen in the two setups is
$2: 3$
$1: 2$
$4: 9$
$9: 4$
Solution
Fringe width, $W=\frac{\lambda \cdot D}{d}$
For constant $\mathrm{W}$ and $\lambda$, $D \propto d$
$\therefore \quad \frac{\mathrm{D}_1}{\mathrm{D}_2}=\frac{\mathrm{d}_1}{\mathrm{~d}_2}=\frac{2}{3}$