In a Young's double slit experiment, a thin sheet of refractive index 1 . 6 is used to cover one slit while a thin sheet of refractive index 1 . 3 is used to cover the second slit. The thickness of both sheets are same and the wavelength of light used is 600 nm . If the central point on the screen is now occupied by what had been the 10 th bright fringe m = 10 , then the thickness of covering sheets is

Question

In a Young's double slit experiment, a thin sheet of refractive index 1 . 6 is used to cover one slit while a thin sheet of refractive index 1 . 3 is used to cover the second slit. The thickness of both sheets are same and the wavelength of light used is 600 nm . If the central point on the screen is now occupied by what had been the 10 th bright fringe m = 10 , then the thickness of covering sheets is, 50 μ m, 8 μm, 20 μ m, 40 μ m

MARKS App · Accepted Answer

When thin sheet is involved then path difference is ∆ x = μ - 1 t for first slit is covered then ∆ x 1 = μ 1 - 1 t = 1 . 6 - 1 t = 0 . 6 t And for second slit covered, ∆ x 2 = μ 2 - 1 t = 1 . 3 - 1 t = 0 . 3 t Now given that central maxima is occupied by 10th bright fringe, ∴ ∆ x = 10 λ = 0 . 6 t - 0 . 3 t = 0 . 3 t ∴ t = 10 λ 0 . 3 = 10 × 600 × 10 - 9 0 . 3 = 2 × 10 - 7 m ∴ t = 20 μ m

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