In Young’s double slit experiment the separation d between the slits is 2 mm , the wavelength λ of the light used…

Q: In Young’s double slit experiment the separation d between the slits is 2 mm , the wavelength λ of the light used 5896 A° and distance D between the screen and slits is 100 cm . It is found that angular width of fringe is 0.20° . To increase the angular fringe width to o.21° (with same λ and D) the separation between the slits needs to be changed to

(a) 2.1 mm

(b) 1.7 mm

(c) 1.9 mm

(d) 1.8 mm

Ans: (d)

Sol: Angular fringe width $ \displaystyle \theta = \frac{\lambda}{d}$

$ \displaystyle 0.20 = \frac{\lambda}{2}$

$ \displaystyle 0.21 = \frac{\lambda}{d}$

On solving ,

d = 1.9 mm