Question

When light of a certain wavelength is incident normally on a certain diffraction grating the line of order 1 is at a diffraction angle of 25 degrees. The diffraction angle of the second order line is :
a) 25
b) 42
c) 50
d) 58
e) 75

I am not sure how to do this problem since it does not have enough information to use the diffraction equations in the book. So, I do not know how to handle the problem.

Thank you


n lambda = d sin( theta )
Since the order n doubles from 1 to 2, so does the sine of the diffraction angle. Find the angle that has twice the sine of 25 degrees. It is not 50 degrees.

Answer 1

d) 58

you said find the angle that is double sin25 (not sin50)

so 2 x sin 25 gets you .84523

find what angle that is using inverse sin

sin^-1 (.84523) = 57.697