Question

grating spectrometer lab

Explain why you would never be able to see a high order of (like say m - 7) in this lab HTML Editor 4 ΒΙ Ο Α I E3 DT 114 12pt Paragraph P O words

Answer 1

Answer:

Let us look at the grating equation for normal incidence: $\boxed{a\sin\theta_m=m\lambda}$

As the number of grooves in the grating is very very large, a typical value is say 500000, the value of a = 1 / 500000 = 2 x 10^(-6) is very very small, so, the number of visible orders in practical life will be fewer! Also, there is a drastic fall in intensity for orders higher than 2 (on either side of m = 0 order) in practical, so, higher orders like m = 7 are really very very faint. Moreover, such higer orders like m = 7 are practically 'out of view' for our arrangement of the spectrometer telescope lens. Therefore, all these reasons combined, it becomes practically impossible to observe higher orders in diffraction grating and normally we cannot even properly observe orders beyond m = 2.

Cheers!