A screen is separated from a double-slit source by 1.50 m. The distance between

Question

A screen is separated from a double-slit source by 1.50 m. The distance between the two slits is 0.0500 mm. The second-order bright fringe (m = 2) is measured to be 3.4 cm from the centerline. Determine the wavelength of the light and the distance between adjacent bright fringes. Calculate the minimum thickness of a soap-bubble film (n= 1.33) that will result in constructive interference in the reflected light if the film is illuminated by light with wavelength 540 nm in free space, Recalculate the minimum thickness for constructive interference when the soap-bubble film is on top of a glass slide with n= 1.5.

Explanation / Answer

1. a) so y = m lambda L/d

so 3.4E-2 = 2*lambda*1.5/0.05E-3

lambda = 5.67E-7 m or 567 nm

b) y = m lambda L/d = 1*5.67E-7*1.5/0.05E-3 = 1.7E-2 m or 1.7 cm

2) a)

so one low to high (1 to 1.33)

so constructive is (m +1 /2) lambda/n = 2 d

min is m = 0

d = lambda/(4n)= (540/(4*1.33))= 101.5 nm

b) now two low to highes 1 to 1.33 and 1.33 to 1.5

so m lambda /n= 2 d

now min is m = 1

d = lambda/(2n) = 540/(2*1.33) = 203 nm

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