(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

12 Light consisting of two wavelengths which differ by 160 nm passes through a diffraction grating with 2.50 x 10^{5}lines per metre. In the diffracted light, the third order of one wavelength coincides with the fourth of the other. What are the two wavelengths and at what angle of diffraction does this coincidence occur?

2. Relevant equations

y=n[tex]\lambda[/tex]L/d I think is what I should be looking at??

3. The attempt at a solution

[tex]\Delta[/tex][tex]\lambda[/tex]=160*10^-9

d=1/2.5*10^5 = 4*10^{-6}not sure if this part is right

If my d is right I think that what I should do next is

y_{3}=3*[tex]\lambda[/tex]*L/4*10^-6

y_{4}=4*[tex]\lambda[/tex]*L/4*10^-6

these are both bright fringes but maybe one should be dark???

That is as far as I get at the moment!

Thanks for any help.

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# Light - Difraction

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