Question

Greatest number of maxima from slit separation diffraction grating

Answer 1

Answer:

Explanation:Light of wavelength λ is incident normally on a diffraction grating that has slit separation of 7λ/2. What is the greatest number of maxima that can be observed using this arrangement.

A. 4

B. 6

C. 7 (answer)

D. 9

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My attempt:

using the diffraction grating formula nλ=dsin(x)

x=90 degrees as can show all possibilities of finding maximas

rearange to n=d/λ

substitute d back to get n=7/2, the answer indicates we have multiplied n by 2, i do not really understand why?

Edit: I get it now. when angle is 90 it looks for all maximas in the half of the segment, so you multiply it by two so you know the máximas in both segments, this works since interference patterns are symmetrical