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Unformatted text preview: 37. Bright interference fringes occur at angles θ given by d sin θ = mλ, where m is an
integer. For the slits of this problem, we have d = 11a/2, so
a sin θ = 2mλ/11
(see Sample Problem 36-5). The first minimum of the diffraction pattern occurs at the
angle θ1 given by a sin θ1 = λ, and the second occurs at the angle θ2 given by a sin θ2 =
2λ, where a is the slit width. We should count the values of m for which θ1 < θ < θ2, or,
equivalently, the values of m for which sin θ1 < sin θ < sin θ2. This means 1 < (2m/11) <
2. The values are m = 6, 7, 8, 9, and 10. There are five bright fringes in all. ...
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