# Question: for an aperture consisting of two parallel slits of width...

###### Question details

For an aperture consisting of two parallel slits of width 0.2 mm whose centres are separated by separated 0.4 mm, illuminated with light of 633 nm, find the angular positions of the first 3 maxima on either side of the central maximum in the Fraunhofer pattern. How many principle maxima will be visible?

My attempt was using the equation $a\mathrm{sin}{\theta}_{mI}={m}_{I}\lambda $, thus:

$0.4\mathrm{sin}{\theta}_{1}=1*633*{10}^{-6}\phantom{\rule{0ex}{0ex}}\mathrm{sin}{\theta}_{1}=0.0015825\phantom{\rule{0ex}{0ex}}{\theta}_{1}=0.091\xb0$

$0.4\mathrm{sin}{\theta}_{2}=2*633*{10}^{-6}\phantom{\rule{0ex}{0ex}}{\theta}_{1}=0.181\xb0$

$0.4\mathrm{sin}{\theta}_{3}=3*633*{10}^{-6}\phantom{\rule{0ex}{0ex}}{\theta}_{1}=0.0272\xb0$

Am I on the right track here? What about the second question: How many principle maxima will be visible?

How do I find that out?

Thank you