Solved Numerical Problem No.1 ( Unit-9: Physical Optics); HSSC-1 (Class-11); Physics (New Book/KPK Text Board, Peshawar) With Verified Answers

In a young double slit experiment the separation of the slits is 1 mm and red light of wavelength 620 nm is falling on it. Determine the distance between the central bright band and the fifth bright fringe on the screen which is 3m away from the slit. (9.3 mm)

Given:

Separation between the slits = d = 1 mm = 1 ｘ 10⁻³ m

Wavelength = λ = 620 nm = 620 ｘ 10⁻⁹ m

Distance between Slit and screen = L = 3 m

Order of bright fringes = m = 5

Distance between the central bright band and the fifth bright fringe = `\ (Yₘ)_{bright}` = ?

For `m^{th}` bright fringe we have

`\ (Yₘ)_{bright}` = m L `\frac {λ}{d}`

by putting values

`\ (Y₅)_{bright}` = 5 ｘ 3 m ｘ `\frac {620 ｘ 10⁻⁹ m}{1 ｘ 10⁻³ m}`

`\ (Y₅)_{bright}` = 15 m ｘ 620 ｘ 10⁻⁶

`\ (Y₅)_{bright}` = 930o ｘ 10⁻⁶ m

`\ (Y₅)_{bright}` = 9.3 ｘ 10⁻³ m

`\ (Y₅)_{bright}` = 9.3 mm -------------Ans

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