How many lines per millimetre should the grating have if for the first order, observed at a wavelength λ = 500 nm, the reflected beam is observed at 10 deg from the normal, the incident angle being 60 deg?(adsbygoogle = window.adsbygoogle || []).push({});

I've done the question and just want to know if I've done anything wrong, as my answer seems too big.

mλ = d(sin i + sin θ)

d = mλ/(sin i + sin θ)

d = (1 x 500 x 10^-9)/(sin 60 + sin 10)

d = 4.809 x 10^-7 m (distance between slits)

No. of lines per m = 1/(4.809 x 10^-7)

=> No. of lines per mm = 1/(4.809 x 10^-7 x 10^-3) = 2.079 x 10^9

Thanks.

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# Homework Help: Diffraction grating lines question

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