In a double slit experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the plane of slits. If the screen is moved by 5 × 10 - 2 m towards the slits, the change in fringe width is 3 × 10 - 3 cm. If the distance between the slits is 1 mm, then the wavelength of the light will be ____________ nm. Numerical answer type. Work it out, then open the answer.

Answer: 600. Δβ = (λ Δ D)/(d) ⇒ λ = (Δβ d)/(Δ D) λ = 3×10⁻⁵ × 1×10⁻³5×10⁻² = 6×10⁻⁷ m So λ = 600 nm.

In a double slit experiment with monochromatic light, fringes are… | JEE Main 2022 (29 Jun, Shift 2)

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YDSE: Fringe Width & Fringe Positions

In a double slit experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the plane of slits. If the screen is moved by 5 $\times$ 10 $-$ 2 m towards the slits, the change in fringe width is 3 $\times$ 10 $-$ 3 cm. If the distance between the slits is 1 mm, then the wavelength of the light will be ____________ nm.

Numerical answer type. Work it out, then open the answer.

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Answer: 600

$\Delta\beta = \frac{\lambda\,\Delta D}{d} \Rightarrow \lambda = \frac{\Delta\beta\, d}{\Delta D}$
$\lambda = \frac{3\times10^{-5} \times 1\times10^{-3}}{5\times10^{-2}} = 6\times10^{-7}\text{ m}$
So $\lambda = 600$ nm.

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