19. Consider the given arrangement. The two slits S and S are illuminated by monochromatic light of wavelength A. Slits S3 and S4 are at separation d minimum intensity on the screen will be 2.D = then ratio of maximum and 3d' P 55 S D 5 SA D Screen (b) 8:1 (d) 2:1 20. A sine wave is travelling in a medium. The minimum distance between the two particles. always having same speed, is (a) 9:1 (c) 4:1 AAN (a) (c) (b) (d)