Coherent monochromatic light of wavelength 632.8 nm passes through a pair of thi
ID: 1289159 • Letter: C
Question
Coherent monochromatic light of wavelength 632.8 nm passes through a pair of thin parallel slits. The figure shows the central portion of the pattern of bright fringes viewed on a screen 1.40 m beyond the slits. What is the distance between the two slits?
Coherent monochromatic light of wavelength 632.8 nm passes through a pair of thin parallel slits. The figure shows the central portion of the pattern of bright fringes viewed on a screen 1.40 m beyond the slits. What is the distance between the two slits?Explanation / Answer
9 fringes cover 2.52 cm, so the distance between 2 successive fringes is, x = 2.52/8 = 0.315 cm
Condition for a bright fringe to occur in a double slit experiment is,
n.lambda/d = x/L
where n is the fringe order (the center being n = 0), d = distance between the slits, L = distance to the screen.
for n = 1
-> d = lambda.L/x = 632.8 x 10^-9*1.4/(3.15 x 10^-3) = 281 x 10^-6 m = 0.281 mm