Find the wavelength of the Light?

Question

A diffraction grating with 600 lines/mm produces a third order interference pattern at 60.5 degrees. find the wavelength of the light source.

Answer 1

The critical equation is d(sin(θm) + sin(θi)) = mλ, where λ is the wavelength of the light (your unknown), θm is the m order diffraction angle (given, 60.5 degrees for given m = 3), θi is the incident angle of the light (assumed to be 0 degrees), and d is the width between diffraction slits (1mm / 600 = 0.0017 mm = 1.7 um).

The equation becomes 1.7(sin(60.5) + sin(0)) = 3λ, where λ is your only unknown and can be easily solved for algebraically. Note that the units are now um (1 x 10^-6 m), and wavelengths of light are usually on the order of 100 nm (visible light is 400 to 700 nm), or 0.1 um, so make sure you report the answer in the correct units. Also take care that your calculator is treating the angle measures as degrees and not radians.

Answer 2

i studied it in my bachelors degree....in optical communication courses...... But cant remeber now