# Maxima & Minima with Diffraction?

Discussion in 'MCAT Study Question Q&A' started by nfg05, Jun 15, 2008.

1. ### nfg05

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The Kaplan Physical Science Review Notes (p. 348 and 349 for anyone who currently has them) confused me. First they talk about diffraction when light passes through a small slit and say:

The location of the dark fringes (minima) is given by the following formula:
(a)sin(theta) = n(lambda)

Then, on the next page when talking about interference and Young's double slit experiment they list the maxima as (d)sin(theta) = m(lambda) and minima as (d)sin(theta) = (m+1/2)(lambda).

In these two formulas, d and a are the same thing (the width of the slit). So which is it? It seems the two discussions are contradicting each other, so did Kaplan mess up or am I missing something here?

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3. ### cwfergus

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I woul dhave to look over my physics II stuff but if i remember correctly,

a --> The width of the SINGLE slit
d --> The distance between the two slits (or multiple if it is a diffraction grating)

They are different for single and double slit

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yes

5. ### nfg05

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Thanks a bunch for clearing that up, I'll blame it on the poorly labeled diagrams in Kaplan which make the two situations look exactly the same. Although they do say it is a double slit experiment in the 2nd case, their diagram and marking of d looks the same as the previous one with its marking of a. They don't even show multiple slits on the diagram

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