Two thin parallel slits that are 1.29 Times 10^-2 mm apart are illuminated by a

Question

Two thin parallel slits that are 1.29 Times 10^-2 mm apart are illuminated by a laser beam of wavelength 580 nm. On a very large distant screen, what is the total number of bright fringes (those indicating complete constructive interference), including the central fringe and those on both sides of it? Solve this problem without calculating all the angles! (What is the largest that sin theta can be? What does this tell you is the largest value of m?) At what angle, relative to the original direction of the beam, will the fringe that is most distant from the central bright fringe occur?

Explanation / Answer

A. m = d*sinA/lambda

for sinA = 1

m = d/lambda = 0.0129*10^-3/(580*10^-9) = 22.24

Therefore, the largest m for fringes on the screen is m =22

There are 2(22) +1 = 45 bright fringes, the central one and 22 above and 22 below it..

The most distant fringe has m = +/- 22

sinA = m*lambda/d = 22*580*10^-9/(0.0129*10^-3)

sinA = 0.989

A = 81.55 deg

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