- #1

physicoo

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I basically did an experiment on diffraction grating, involving looking through a diffraction grating and observing the spectra, aiming a laser beam at the grating etc.

What I would like to clarify is:

1) Suppose a grating with more lines per unit length (meaning the grating constant d, decreases) is used, I assume the angles and spread of spectra both increase, mainly due to the grating equation of d.sin(theta) = m(lambda)?

2) Now suppose the wavelength of light used is increased (E.g. From green to red), similarly to the previous question, I am again assuming the angles and spread of spectra also increases, again due to the grating equation.

3) I understand that there is a limit to the order of spectrum that can be observed in diffraction grating, and I've read that it's primarily because the angle theta cannot exceed 90 degrees, so the limit of the order is mainly (grating constant/wavelength). Could anyone explain to me why it can't exceed 90 degrees?

Appreciate the help! :)