Question

In Young's double slit experiment, 62 fringes are seen in visible region for sodium light of wavelength 5893 Å. If violet light of wavelength 4358 Å is used in place of sodium light, then number of fringes seen will be
(a) 54(b) 64(c) 74(d) 84

Answer 1

Answer:

84

Explanation:

The number of fringes seen will be 84.

For sodium light,

Length of the region = No. of fringes × Fringe width

As fringe width = Dλ/d

As 'D' [distance between source and screen] and 'd' [distance between the slits] are constant throughout the experiment, so fringe width depends on λ, wavelength only.

λ = 5893A

No. of fringes = 62

∴ Length of the region = (5893 × 62) A

For violet light,

Length of the region is same as that for sodium light.

So, length of region = (5893 × 62) A

Wavelength of violet light = 4358 A

So, no. of fringes = (Length of region)/(Wavelength)

                             = (5893 × 62)/4358 = 83.8 ≈ 84

84 fringes are observed for violet light.