In a double-slit interference experiment, the slit separation is 0.30 mm and the screen is 2.5 m away. Light of wavelength 500 nm is used. What is the distance between the central bright fringe and the first-order bright fringe on the screen?
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Correct answer
B. 4.2 mm
Principle or equation
For small angles in double-slit interference, the position of the m-th bright fringe is y_m = m λ L / d.
Why this answer is correct
For m = 1: y = (1)(500×10^-9 m)(2.5 m) / (0.30×10^-3 m) = 4.17×10^-3 m = 4.2 mm.
Example
With d = 0.50 mm, L = 3.0 m, λ = 450 nm, y_2 = 2×450×10^-9×3.0 / 0.50×10^-3 = 5.4 mm.
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