18.A sine wave is travelling in a medium. The minimum distance between the two particles, always having same speed, is (1) (2) (3) 2 (4) 2 19.A radioactive -emission. A detector records n -particles in 2s and by next 2s (accumulatively) it records 1.1 n-particle. Number of -particles recorded by detector after a long time, is (1) 11n 10 12n (2) 10 10n (3) 2n 20.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 be = then ratio of maximum and minimum intensity on the screen will 3d' (1)9:1 (3) 4:1 failisha SA D D Screen (2) 8:1 (4) 2:1