Question

There is an incident beam of light toward an opening in a grating. The light breaks into 5 different paths labeled n = 2, n = 1, n = 0, n = 1 and n = 2. The angle between the boundary and n = 2 is labeled A. The angle between n = 0 and n = 1 is labeled B. The angle between n = 1 and n = 2 is labeled as C.
Which angle (A, B, or C) is the diffraction angle?

Answer 1

B.

Reason: the diffraction angle θn is the angle between the zero-order (n = 0) beam and the nth-order beam (or equivalently between the grating normal and the nth-order beam when incidence is normal). In your diagram the angle between n = 0 and n = 1 is labeled B, so B is the diffraction angle (θ1). The grating equation is d sin θn = nλ.