In a Young's double slit experiment, a laser light of 560 nm produces an interference pattern with consecutive bright fringes' separation of 7.2 mm. Now another light is used to produce an interference pattern with consecutive bright fringes' separation of 8.1 mm. The wavelength of second light is__________nm.

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Vishal Baghel | Contributor-Level 10

6 months ago

$λ_{1} = 560 n m,$ fringe width, B = 7.2 mm

$\Rightarrow B_{1} = \frac{D λ_{1}}{d} = 7.2 m m$

For $λ_{2} \to B_{2} = \frac{D λ_{2}}{d} = 8.1 m m$ $_{}_{} \frac{_{}}{}$

$\frac{B_{2}}{B_{1}} = \frac{λ_{2}}{λ_{1}} = \frac{8.1}{7.2} \Rightarrow λ_{2} \frac{81}{72} λ_{1}$

$= \frac{9}{8} * 560 n m$

= 630 nm

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3d = 0.6mm

D = 80cm

= 800mm

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$\Rightarrow \frac{d y}{D} = (2 n + 1) \frac{λ}{2}$ [for Dark fringe at P]

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