In a Young's double slit experiment, the slits are placed 0.320 mm apart. Light of wavelength λ = 500 nm is incident on the slits. The total number of bright fringes that are observed in the angular range - 30° ≤ θ ≤ 30° is: (a) 640 (b) 320 (c) 321 (d) 641

Answer: (d). Bright fringe: dsin θ = nλ. nmax = (dsin 30°)/(λ) = 0.32×10⁻³× 0.5500×10⁻⁹ = 320. Fringes on each side: 320, plus the central one: 2(320)+1 = 641. So the answer is (d) 641.

In a Young's double slit experiment, the slits are placed 0.320 mm… | JEE Main 2019 (9 Jan, Shift 2)

Q62JEE Main 2019 · 9 JAN · SHIFT 2Difficult

YDSE: Film, Medium & Two Wavelengths

In a Young's double slit experiment, the slits are placed 0.320 mm apart. Light of wavelength $\lambda$ = 500 nm is incident on the slits. The total number of bright fringes that are observed in the angular range $-$ 30° $\le \theta \le$ 30° is:

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Answer: (d)

Bright fringe: $d\sin\theta = n\lambda$ .
$n_{max} = \frac{d\sin 30^\circ}{\lambda} = \frac{0.32\times10^{-3}\times 0.5}{500\times10^{-9}} = 320$ .
Fringes on each side: 320, plus the central one: $2(320)+1 = 641$ .
So the answer is (d) 641.

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