# Help w/ diffraction grating

Ok, so I'm going to have a lab final on diffraction gratings tomorrow, and I want to make sure I have the right idea. Basically we need to find out the wavelength of an unknown light using a diffraction grating.

So let's say the grating is perpendicular to the light, and the distance from the grating to the light is 1m. The distance from the zero order line (the light source?) and first order line (first maxima on the right?) is .5m. That would mean that theta is 26.6 degrees, correct? And with 1000 lines per cm (1/d), the equation m*wavelength=d*sin(theta) would be as follows:

1*wavelength=(1/1000)*sin(26.6)

making wavelength=4.48*10^-4 cm. Is this correct?

Also, is it possible to find wavelength without d? Because I'm not even sure if we're going to be given it or not.

## Answers and Replies

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Kurdt
Staff Emeritus
Science Advisor
Gold Member
That seems fine. If you're doing an experiment the grating should have on it somewhere how many lines it has per cm etc.

Alright, thanks a lot!