In a double-slit interference experiment, the slit separation is 0.50 mm and the screen is 2.0 m away. Light of wavelength 600 nm is used. What is the distance between the central bright fringe and the second-order bright fringe? (Assume small angles.)
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Correct answer
B. 4.8 mm
Principle or equation
For double-slit interference, the position of the m-th bright fringe is y_m = m λ L / d.
Why this answer is correct
Given d = 0.50 mm = 5.0e-4 m, L = 2.0 m, λ = 600 nm = 6.0e-7 m, m = 2. y_2 = 2 * (6.0e-7) * 2.0 / (5.0e-4) = 2 * 1.2e-6 / 5.0e-4 = 2.4e-6 / 5.0e-4 = 4.8e-3 m = 4.8 mm.
Example
For m = 1 with same parameters, y_1 = 2.4 mm.
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