00:01
So in this problem, we want to show that the third -order violet end of the spectrum always overlaps with the second -order right end of the spectrum in the diffraction pattern for the polychromatic source diffraction that is independent of spacing between the lines in the grading elements.
00:19
So first of all, we need to know that the visible spectrum is typically between 400 nanometer to 750 nanometer, where the 400 nanometer one is the violet end, which i'm labeling here as lambda v, and the 750 nanometer one is the rate wavelength, that corresponds to the maximum wavelength of the rate color.
00:49
Now, from the condition for the maximum in the diffraction of the grading, we know that sine theta equals m lambda over d right so for the violet end for the third order this is going to be sign theta 3 v equals 3 lambda v over d which is 400 times 3 right so so it's going to be, i'm just going to write down this 3 times 400 nanometer over d is d.
01:37
Let's just leave it that way right now.
01:42
And for the rate end, sine theta 2 of red, equals 2 lambda rad over d, which equals 2 times 750 times 750 times.
02:02
10 to the negative 9 over d.
02:07
So i can actually write this down as 1 ,200 nanometer over d...