61. When a thin glass plate (n = 1.5) is introduced in one of the arm of Michelson Interferometer using light of wavelength 5890 , there is a shift of 10 fringes. The thickness of plate is (1) 2.95 m (2) 5.89 m (3) 8.85 m (4) 11.8 m 62. r is radius of first circle in zone plate and is wavelength of light used. First focal length of zone plate will be (1) 122 e (2) 2 (3) 22 (4) 2 63. The ratio of spontaneous emission coefficient to stimulated emission coefficient is proportional to nth power of frequency of photon. Here value of n is (1) 0 (3) 2 (2) 1 (4) 3 64. The pumping method in Ruby Laser is (1) optical pumping (2) electron impact (3) chemical pumping (4) gas dynamic pumping 65. According to uncertainty principle, the manimum energy of electron, for its existence in side nucleus, should be approximately (1) 4 MeV (2) 20 MeV (3) 400 MeV (4) 5000 MeV