Question

In a biprism experiment, fringe width is 0.4 mm when the eyepiece is at a distance of 1 m from the slit. If the eyepiece is moved through a distance of 25 cm towards biprism without changing any other arrangement then the change in fringe width is

• A. 0.1 mm
• B. 0.2 mm
• C. 0.15 mm
• D. 0.25 mm

Answer 1

The correct option is A 0.1 mm

$X=\frac{D\lambda }{d}0.4=1\times \frac{\lambda }{d}⟶1x=0.75\frac{\lambda }{d}⟶21-0.25=0.75\frac{equation1}{equation2}\Rightarrow \frac{0.4}{x}=\frac{\frac{1}{3}}{4}=\frac{4}{3}x=\frac{3\times 0.4}{4}=0.3$

Difference in fringe width $=0.4-0.3=0.1$mm