(a) Figure 36.16 shows plane waves of light incident normally on a diffraction grating. If instead the light strikes the grating at an angle of incidence θ' (measured from the normal), show that the condition for an intensity maximum is not Eq. (36.13), but rather d(sin θ + sin θ’) = mλ (m = 0, ±1, ±2, ±3, . )
(b) For the grating described in Example (Section 36.5), with 600 slits/mm. find the angles of the maxima corresponding to m = 0, 1, and – 1 with red light (λ = 650 urn) for the cases θ' = 0 (normal incidence) and θ' = 20.00.