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# Physics diffraction grating question watch

1. A diffraction grating has 300 lines per mm. It is illuminated with monochromatic light of wavelength 540nm. Calculate the angle of the 2nd order maximum giving your answer to the appropriate number of significant figures.

So far i know you use the equation dsin(theta) = n-lambda and then rearrange for sin(theta), my calculations are 540*10^-9(*2)/3.3*10^-6 and then the answer i do is sin^-1(ans) to get the angle 1.875...*10^-11

But the answer in the mark scheme is 18.9 degrees i dont understand what i did wrong, maybe its something obvious.
2. (Original post by RS012)
A diffraction grating has 300 lines per mm. It is illuminated with monochromatic light of wavelength 540nm. Calculate the angle of the 2nd order maximum giving your answer to the appropriate number of significant figures.

So far i know you use the equation dsin(theta) = n-lambda and then rearrange for sin(theta), my calculations are 540*10^-9(*2)/3.3*10^-6 and then the answer i do is sin^-1(ans) to get the angle 1.875...*10^-11

But the answer in the mark scheme is 18.9 degrees i dont understand what i did wrong, maybe its something obvious.
I think you have made an error in entering everything into your calculator. I have used the same numbers as you and got the correct answer. Your answer is quite far out for it to be simply due to your calculator being in radians, although I would also check to see if you're in degrees.

I typed into my calculator: and got the correct answer.

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Updated: February 2, 2017
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