Physics Mcqs

 

1. Radius of atom is about 5 times the radius of nucleus

2. Nucleus consists of nucleons(protons and neutrons)

3. A proton has a positive charge equals to 1.6×10-19C

4. Atomic no. = no. Of protons = Z

5. Atomic mass = p + n = A

6. In initial light elements n = p

7. In heavy elements n > p

8. Stability depends upon no. of neutron

9. 1amu = 1.67 × 10-27kg = 931 Mev

10. 1amu = mass of C-12/12

11. An atom on the whole is electrically neutral

12. Binding energy is the amount of energy that must be supplied to a nucleus if nucleus is to be broken up into protons and neutrons

13. B.E/nucleon = mass defect × c²/A

14. Mass defect = Zmp + (A-Z) mn - mnucleus

15. B.E/nucleon ist increases then decreases

16. B.E/nucleon is maximum for Fe-58 = 8.8Mev

17. B.E/nucleon is minimum for U-238 = 7.6Mev

18. Iron is most stable element

19. B.E for deutron = 2.23MeV = 1.2×10-¹²J

20. B.E for tritium = 7.97MeV

21. B.E for Helium = 28.2 MeV

22. Beta particle is a fast moving e- that come out of nucelus

23. Beta decay oocurs when n/p ratio is too high

24. Alpha decay occurs when n/p ratio is too low

25. Alpha and beta emission occurs when nucleus undergoes excitation

26. Gama decay occurs when nucleus undergoes dexcitation

27. Radioactivity is purely a nuclear phenomenon. This is not affected by chemical or physical reaction

28. During nuclear changes, law of conservation of mass, energy, momentum and charge remains applicable

29. In alpha decay, mass no. And charge no. both are decreases by 4 and 2 respectively

30. Emission of alpha particle from radium-226 gives radon-222

31. In beta decay, mass no. does not change while charge no. is increased by 1.

32. The emission of beta particle from Polonium-218 gives Astatine-218

33. The emission of beta particle from Thorium-234 gives Protactinium-234

34. Emission of alpha particle from uranium-238 gives Thorium-234

35. Gama radiation is simply a photon that has neither any charge nor any mass. So no change in mass no. and charge no. will occur with its emission

36. Radioactive decay process is quite random so we cannot tell about any particular atom as to when will it decay

37. Decay rate is inversly proportional to half-life

38. Activity is directly proportional to half-life A=λN (here λ is decay constant)

39. Decay constant is directly proportional to no. of decaying atoms. Delta N = - λN t

40. Unit of decay constant is s-¹

41. Mean life > Half life

42. Mean life = 1/λ

43. λT½ = 0.693

44. T½ = Tmean (0.693/λ)

45. No. of half lifes = Total time/half life

46. Undecayed = N°/2n (here n is power of 2)

47. Decayed = total - undecayed

48. Example 21.2

49. Half life of

Radon = 3.8 days

U-239 = 23.5 mint

U-238 = 4.5×109 years

I-131 = 8 days

I-125 = 60 days

Np = 2.4 days

Pu = 24000 years

Na-24 = 15 hours

Fe-59 = 45 days

50. Range of beta particle is 100 times greater than alpha particle

51. Ionizing ability of beta particle is 100 times less than alpha particle

52. Alpha particle is about 7000 times massive than an e- thats why it does not suffer appreciable deflection from its straight path

53. At energy less than 0.5MeV, photoelectric effect is dominant

54. At energy more than 1.02MeV, pair production is dominant

55. Intensity of gama rays falls off as the inverse square of distance from source

56. 𝐠 −particle ionizes an atom due to electrostatic attraction and due to direct elastic collision

57. Typical source of alpha particle is Radon-222

58. Typical source of beta particle is Strontium-94

59. Typical source of gama rays is Cobalt-60

60. Gamma rays are absorbed by lead sheet.

61. Gamma rays are more penetrating as compared to alpha and beta particle

62. Neutrons are more penetrating than gamma rays

63. Ionizing ability of alpha particle > beta particle > gamma rays > neutrons

64. He+² is an alpha particle

65. Only alpha particles emit with same energy while beta particles and gamma rays emit with variable energy

66. When alpha particle strikes with 7N-14 then we get one proton and 8O-17

67. In nuclear fission, 1MeV/nucleon energy is released

68. In nuclear fusion, 6.4MeV/nucleon energy is released

69. U-235 : naturally occuring 0.7%. usually fissionable with thermal neutron or slow neutron. % increase in fuel 2-4%

70. Plutonium-239 : fission with Slow neutron is easy

71. U-238 = 99%

72. fission chain reaction is controlled by cadmium rod because these rods are capable of absorbing large no. Of neutrons

73. Now-a-days Plutonium-239 and Uranium-233 are also being used as fuel

74. In nuclear reaction, heavy water is used as moderator to slow down neutrons

75. No. of neutrons are controlled by Cadmium or boron rods in nuclear reactor

76. For fission reactions, ratio of mass of products to mass of reactants is less than 1

77. Fast reactors are designed to make use of U-238 which is about 99%

78. Plutonium can be fissioned by fast neutron

79. Moderators are not needed in fast reactors

80. Do U Know?

U-238..... >U-238..... >Np..... >Pu

This sequence follows emission of gamma, beta+gamma, beta+gamma. 3 gamma 2 beta particles

81. When two deutrons are merged to form a helium nucleus, 24MeV energy is released

82. When deutron and tritium are merged, 17.6MeV energy is releaed

84. Subatomic particles are divided into three groups

a. Photons

b. Leptons (e-, muons)/do not experience strong nuclear force

c. Hadrons (n, mesons, p)/experience strong nuclear force

85. Meson = 1Quark and 1Antiquark

86. Meson mass equal or greater than protons

87. Baryon = 3 Quarks

88. Baryon mass lighter than protons

89. Proton = 2up Quarks + 1down Quark

90. Neutron = 1up Quark + 2 down Quark