MockTime.com. Ans: (b) Q6. Curie is a unit of [1989] (a) energy of gamma-rays (b) half-life (c) radioactivity (d) intensity of gamma-rays Ans: (c)

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1 Chapter Nuclei Q1. A radioactive sample with a half life of 1 month has the label: Activity = 2 micro curies on What would be its activity two months earlier? [1988] 1.0 micro curie 0.5 micro curie 4 micro curie 8 micro curie Q2. [1988] Q3. A radioactive element has half life period 800 years. After 6400 years what amount will remain? [1989] 1/2 1/16 1/8 1/256 Q4. Ans: Q6. Curie is a unit of [1989] energy of gamma-rays half-life radioactivity intensity of gamma-rays Ans: Q7. The average binding energy of a nucleon inside an atomic nucleus is about [1989] 8 MeV 8 ev 8 J 8 ergs Ans: Q8. The nuclei 6C 13 and 7N 14 can be described as [1990] isotones isobars isotopes of carbon isotopes of nitrogen Ans: Q9. Which of the following statements is true for nuclear forces? [1990] they obey the inverse square law of distance they obey the inverse third power law of distance they are short range forces they are equal in strength to electromagnetic forces. Ans: Q10. The ratio of the radii of the nuclei 13Al 27 and 52Te 125 is approximately [1990] 6: 10 13: 52 40: : 73 Ans: Q11. [1989] A and C are isotopes A and C are isobars A and B are isotopes A and B are isobars Ans: Q5. Ultraviolet radiations of 6.2 ev falls on an aluminum surface. K.E. of fastest electron emitted is (work function = 4.2 ev) [1989] J J J J 7N 14 7N 13 5B 13 6C 13 Ans: [1990] Q12. The constituents of atomic nuclei are believed to be [1991] neutrons and protons protons only electrons and protons electrons, protons and neutrons Ans:

2 Q13. The half-life of radium is 1600 years. The fraction of a sample of radium that would remain after 6400 years [1991] 1/4 1/2 1/8 1/16 Q14. An electron with (rest mass m0) moves with a speed of 0.8 c. Its mass when it moves with this speed is [1991] m 0 m0/6 5m0/3 3m0/5 Ans: Q20. The mass density of a nucleus varies with mass number A as [1992] A 2 A constant 1/A Ans: Q15. In the nucleus of 11Na 23, the number of protons, neutrons and electrons are [1991] 11, 12,0 23, 12, 11 12, 11,0 23, 11, 12 Ans: Q21. [1993] Q16. If the nuclear force between two protons, two neutrons and between proton and neutron is denoted by Fpp, Fnn and Fpn respectively, then [1991] Q17. Solar energy is due to [1992] fusion reaction fission reaction combustion reaction chemical reaction Ans: Q18. The energy equivalent of one atomic mass unit is [1992] J J 931 MeV 9.31 MeV Ans: Q19. The mass of alpha-particle is [1992] less than the sum of masses of two protons and two neutrons equal to mass of four protons equal to mass of four neutrons equal to sum of masses of two protons and two neutron Ans: Ans: Q22. The binding energy per nucleon is maximum in case of [1993] Ans: Q23. [1993] s s s s 1 Ans: Q24.

3 [1994] 19.6 MeV 2.4 MeV 8.4 MeV 17.3 MeV Q25. Heavy water is used as a moderator in a nuclear reactor. The function of the moderator is [1994] to control energy released in the reactor to absorb neutrons and stop chain reaction to cool the reactor to slow down the neutrons to thermal energies. Q26. The mass number of He is 4 and that for sulphur isthe radius of sulphur nuclei is larger than that of helium by [1994] Ans: Q27. The nature of ions knocked out from hot surfaces is [1995] protons electrons neutrons nuclei Ans: Q28. 6 and 8 6 and 6 8 and 8 8 and 6 [1995] Q29. The count rate of a Geiger Muller counter for the radiation of a radioactive material of half-life 30 minutes decreases to 5 sec 1 after 2 hours. The initial count rate was [1995] 20 sec 1 25 sec 1 80 sec sec 1 Ans: Q30. A nucleus ruptures into two nuclear parts, which have their velocity ratio equal to 2 : 1 What will be the ratio of their nuclear size (nuclear radius)? [1996] 2 1/3 : 1 1: 2 1/3 3 1/2 : 1 1: 3 1/2 Ans: Q31. The activity of a radioactive sample is measured as 9750 counts per minute at t =0 and as 975 counts per minute at t = 5 minutes. The decay constant is approximately [1997] per minute per minute per minute per minute Ans: Q32. The stable nucleus that has a radius half that of Fe 56 is [1997] Li 7 Na 21 S 16 Ca 40 Ans: Q33. [1997] 2000 MeV 200 MeV 2 MeV 200 kev Ans: Q34. A free neutron decays into a proton, an electron and [1997] a beta particle an alpha particle an anti-neutrino a neutrino Ans: Q35. The most penetrating radiation of the following is [1997] gamma-rays alpha particles beta-rays X-rays Ans:

4 Q36. Which of the following is used as a moderator in nuclear reactors? [1997] Plutonium Cadmium Heavy water Uranium Ans: Q37. Half-lives of two radioactive substances A and Bare respectively 20 minutes and 40 minutes. Initially, the samples of A and B have equal number of nuclei. After 80 minutes the ratio of remaining numbers of A and B nuclei is [1998] 1: 16 4: 1 1: 4 1: 1 Ans: Q38. Q42. [1999] mass number reduces by 4 mass number reduces by 5 mass number reduces by 6 mass number increases by 4 Ans: Q43. [2000] [1998] 19: 81 10: 11 15: 16 81: 19 Ans: Q39. [1998] n 1X m 4 n 2Y m 4 n 4Z m 4 nz m 4 Ans: Q44. Atomic hydrogen has life period of [2000] one minute one day a fraction of a second Ans: Q45. It is possible to understand nuclear fission on the basis of the [2000] liquid drop model of the nucleus meson theory of the nuclear forces proton-proton cycle independent particle model of the nucleus Ans: Q46. Q40. Ans: Q41. Alpha-particles are [1999] protons positron neutrally charged ionized helium atoms [1998] a proton a neutron a neutrino an electron Ans: [2000] Q47. Mn and Mp represent mass of neutron and proton respectively. If an element having atomic mass M has N- neutron and Z-proton, then the correct relation will be [2001]

5 Ans: Q48. A sample has radioactive nuclei of half life 10 days. The number of atoms decaying in 30 days is [2002] Q49. A deuteron strikes 8O 16 nucleus with subsequent emission of an alpha particle. Identify the nucleus so produced [2002] 3Li 7 5B 10 7 N 13 7 N gm 1.35 gm 2.50 gm 3.70 gm Ans: Q54. The mass number of a nucleus is [2003] sometimes less than and sometimes more than its atomic number always less than its atomic number always more than its atomic number sometimes equal to its atomic number Q55. The mass of proton is u and that of neutron is u (u = atomic mass unit). The binding energy of 4 2He is [2003] u j erg 28.4 MeV Q56. The volume occupied by an atom is greater than the volume of the nucleus by a factor of about [2003] Ans: Q50. For a nuclear fusion process, the suitable nuclei are [2002] any nuclei heavy nuclei light nuclei nuclei lying in the middle of the periodic table Ans: Q51. Solar energy is mainly caused due to [2003] gravitational contraction burning of hydrogen in the oxygen fission of uranium present in the Sun fusion of protons during synthesis of heavier elements Q52. fission E-decay J-decay fusion Ans: [2003] Q53. A sample of radioactive element has a mass of 10gm at an instant t=0. The approximate mass of this element in the sample after two mean lives is [2003] Q57. If in nuclear fusion process the masses of the fusing nuclei be m1 and m2 and the mass of the resultant nucleus be m3, then [2004] m3> (m1 + m2) m3 = m1 + m2 m3 = m1 m2 m3< (m1 + m2) Q58. A protons and (Z-A) neutrons Z neutrons and (A-Z) protons Z protons and (A-Z) neutrons Z protons and A neutrons Ans: [2004] Q59. Mp denotes the mass of a proton and Mn that of a neutron. A given nucleus, of binding energy B, contains Z protons and N neutrons. The mass M(N, Z) of the nucleus is given by (c is the velocity of light) [2004] M(N, Z) = NMn + ZMp + B/c 2 M(N, Z) = NMn + ZMp Bc 2 M(N, Z) = NMn + ZMp + Bc 2 M(N, Z) = NMn + ZMp B/c 2 Q60. The nuclei of which one of the following pairs of nuclei are isotones? [2005]

Fission of nuclei is possible because the binding energy per nucleon in them [2005] increases with mass number at low mass numbers. decreases with mass number at low mass numbers.

6 34Se 74, 31Ga 71 38Sr 84, 38Sr 86 42Mo 92, 40Zr 92 20Ca 40, 16S 32 Ans: Q61. Q66. [2005] a + b + c a + b c c a b c + a b Ans: Q62. [2007] Ans: Q67. [2005] equal to 1 greater than 1 less than 1 depends on the mass of the parent nucleus Ans: Q63. Fission of nuclei is possible because the binding energy per nucleon in them [2005] increases with mass number at low mass numbers. decreases with mass number at low mass numbers. increases with mass number at high mass numbers. decreases with mass number at high mass numbers. [2007] the electrons produced as a result of the decay of neutrons inside the nucleus the electrons produced as a result of collisions between atoms the electrons orbiting around the nucleus the electrons present inside the nucleus Ans: Q68. Q64. [2006] 23.6 MeV 19.2 MeV 30.2 MeV 25.8 MeV Ans: Q65. [2006] [2007] B.E. = [ZMp + (A Z)Mp M(A, Z)]c 2 B.E. = [ZMp + ZMn M(A, Z)]c 2 B.E. = M(A, Z) ZMp (A Z)Mn B.E. = [M(A, Z) ZMp (A Z)Mn ]c 2 Ans: Q69. [2007] 9.6 fm 12.0 fm 4.8 fm 6.0 fm.

7 Q70. [2008] 46 MeV 5.6 MeV 3.9 MeV 23 MeV Ans: [2010] Ans: Q71. M(A, Z) = ZMp + (A Z) Mn BE/c 2 M(A, Z) = ZMp + (A Z) Mn + BE M(A, Z) = ZMp + (A Z) Mn BE M(A, Z) = ZMp + (A Z)Mn + BE/c 2 Ans: [2008] Q72. Two nuclei have their mass numbers in the ratio of 1: 3. The ratio of their nuclear densities would be [2008] 1: 3 3: 1 (3) 1/3 : 1 1: 1 Q73. [2009] Q74. Q75. The activity of a radioactive sample is measured as N0 counts per minute at t =0 and N 0/e counts per minute at t = 5 minutes. The time (in minutes) at which the activity reduces to half its value is [2010] loge 2/ 5 5 /loge 2 5 log102 5 loge 2 Q76. The binding energy per nucleon in deuterium and helium nuclei are 1.1 MeVand 7.0 MeV, respectively. When two deuterium nuclei fuse to form a helium nucleus the energy released in the fusion is: 30.2 MeV 23.6 MeV 2.2 MeV 28.0 MeV Ans: Q77. The decay constant of a radio isotope is λ. If A1 and A2 are its activities at times t 1 and t 2 respectively, the number of nuclei which have decayed during the time (t 1 t 2): Q78. The half-life of a radioactive isotope 'X' is 50 years. It decays to another element 'Y' which is stable. The two elements 'X' and 'Y' were found to be in the ratio of 1: 15 in a sample of a given rock. The age of the rock was estimated to be [2011] 150 years 200 years 250 years 100 years Ans: Q79. The power obtained in a reactor using U 235 disintegration is 1000 kw. The mass decay of U 235 per hour is [2011]

8 10 microgram 20 microgram 40 microgram 1 microgram Ans: Q84. If the nuclear radius of 27 Al is 3.6 Fermi, the approximate nuclear radius of 64 Cu in Fermi is: [2012] Ans: Q80. A radioactive nucleus of mass M emits a photon of frequency Q and the nucleus recoils. The recoil energy will be [2011] Mc 2 hv h 2 v 2 / 2Mc 2 zero hv Ans: Q81. Ans: [2011] Q82. Fusion reaction takes place at high temperature because [2011] nuclei break up at high temperature atoms get ionised at high temperature kinetic energy is high enough to overcome the coulomb repulsion between nuclei molecules break up at high temperature Ans: Q83. Two radioactive nuclei P and Q, in a given sample decay into a stable nucleolus R. At time t =0, number of P species are 4 N0 and that of Q are N0. Half-life of P (for conversion to R) is 1 minute where as that of Q is 2 minutes. Initially there are no nuclei of R present in the sample. When number of nuclei of P and Q are equal, the number of nuclei of R present in the sample would be [2011] 3N0 9N0/2 5N0/2 2N0 Ans: Q85. A mixture consists of two radioactive materials A 1 and A2 with half lives of 20s and 10s respectively. Initially the mixture has 40 g of A1 and 160 g of A2. The amount of the two in the mixture will become equal after: [2012] 60 s 80 s 20 s 40 s Q86. The half-life of a radioactive nucleus is 50 days. The time interval (t 2 t 1) between the time t2 when 2/3 of it has decayed and the time t1 when 1/3 of it had decayed is: [2012] 30 days 50 days 60 days 15 days Ans: Q87. A certain mass of Hydrogen is changed to Helium by the process of fusion. The mass defect in fusion reaction is a.m.u. The energy liberated per a.m.u. is (Given: 1 a.m.u = 931 MeV) [2013] 26.7 MeV MeV MeV 2.67 MeV Ans: Q88. The half life of a radioactive isotope X is 20 years. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio of 1: 7 in a sample of a the given rock. The age of the rock is estimated to be [2013] 60 years 80 years 100 years 40 years Ans: Q89. [2013]

9 Ans: Q90. How does the binding energy per nucleon vary with the increase in the number of nucleons? [NEETKar. 2013] Increases continuously with mass number Decreases continuously with mass number First decreases and then increases with increase in mass number First increases and then decreases with increase in mass number Q1. Q11. Q12. Q13. Q14. Q2. Q15. Q3. Q16. Q4. Q17. Q18. Q19. Q5. Q6. Q7. Q8. Q20. Q9. Q10.

10 Q21. Q29. Q22. Q23. Q30. Q24. Q25. Q31. Q26. Q27. Q28. Q32.

11 Q33. Q39. Q34. Q40. Q35. Q41. Q36. Q42. Q37. Q43. Q38. Q44. Q45.

12 Q46. Q47. Q54. Q55. Q56. Q48. Q57. Q49. Q58. Q59. Q60. Q50. Q61. Q51. Q52. Q62. Q53. Q63.

13 Q64. Q68. Q65. Q69. Q66. Q70. Q67. Q71.

14 Q77. Q72. Q78. Q73. Q74. Q79. Q75. Q76.

15 Q80. Q81. Q82. Q83. Q84. Q85.

16 Q88. Q89. Q90. Q86. Q87.

= : K A

= : K A Atoms and Nuclei. State two limitations of JJ Thomson s model of atom. 2. Write the SI unit for activity of a radioactive substance. 3. What observations led JJ Thomson to conclusion that all atoms have