Question

In Young's double slit experiment the

separation d between the slits is 2 mm, the

wavelength  of the light used is 5896 Å and

distance D between the screen and slits is

100 cm. It is found that the angular width of

the fringes is 0.20°. To increase the fringe

angular width to 0.21° (with same  and D) the

separation between the slits needs to be

changed to

Accepted Answer

**Sol.** $	ext{Angular width} = \frac{\lambda}{d}$

$$0.20^\circ = \frac{\lambda}{2 	ext{ mm}} \quad \dots(i)$$

$$0.21^\circ = \frac{\lambda}{d} \quad \dots(ii)$$

Dividing we get,
$$\frac{0.20}{0.21} = \frac{d}{2 	ext{ mm}}$$

$$	herefore d = 1.9 	ext{ mm}$$