**P. 3851.** A diffraction grating is illuminated by light of wavelength 598 nm. The distance between the lines in the diffraction pattern formed on a screen 5 m away from the grating is 2 cm. Find the distance between two rulings. How would the diffraction pattern change if half of the grating parallel to the rulings, or perpendicular to the rulings was covered?

(5 points)

**Deadline expired on 11 January 2006.**