Light waves emerging from the slits of a diffraction grating are coherent and produce an interference pattern. A narrow beam of light from a laser is incident normally on a diffraction grating, as shown in Fig. 5.1. [Figure 5.1] Spots of light are seen on a screen positioned parallel to the grating. The angle corresponding to each of the second order maxima is 51°. The number of lines per unit length on the diffraction grating is 6.7 x 10⁵m⁻¹.