Page 1 Exercises For JEE Main Subjective Questions Note You can take approximations in the answers. Radioactivity Q 1. The disintegration rate of a certain radioactive sample at any instant is 4750 disintegrations per minute. Five minutes later the rate becomes 2700 per minute. Calculate (a) decay constant and (b) half-life of the sample Q 2. A radioactive sample contains l.00 × 10 15 atoms and has an activity of 6.00 × 10 11 Bq. What is its half-life? Q 3. Obtain the amount of 60 Co necessary to provide a radioactive source of 8.0 Ci strength. The half-life of 60 Co is 5.3 years? Q 4. The half-life of 238 92 U against alpha decay is 4.5 × 10 9 year. How much disintegration per second occurs in 1 g of 238 92 U ? Q 5. What is the probability that a radioactive atom having a mean life of 10 days decays during the fifth day? Q 6. In an ore containing Uranium, the ratio of 238 Uto 206 Pb nuclei is 3. Calculate the age of the ore, assuming that all the lead present in the ore is the final stable product of 238 U. Take the half-life of 238 U to be 4.5 × 10 9 years. Q 7. The half-lives of radioisotopes P 32 and P 33 are 14 days and 25 days respectively. These radioisotopes are mixed in the ratio of 4 :1 of their atoms. If the initial activity of the mixed sample is 3.0 m Ci, find the activity of the mixed isotopes after 60 year. Nuclear Reactions Q 8. Complete the following reactions. (a) 226 88 Ra ? ? ? (b) 19 19 89 OF ?? (c) 25 25 13 12 AI Mg ?? Q 9. Consider two decay reactions. (a) 236 206 92 82 U Pb ?? 10 protons + 20 neutrons (b) 236 206 4 92 82 2 U Pb 8 He ? ? ? 6 electrons Are both the reactions possible? Q 10. Obtain the binding energy of a nitrogen nucleus from the following data : m H = 1.00783 u, m N = 1.00867 u, 14 7 m( N) = 14.00307 u Give your answer in units of MeV. [Remember 1 u = 931.5 Me V/c 2 ] Q 11. 8 protons and 8 neutrons are separately at rest. How much energy will be released if we form 16 8 O nucleus? Given: Mass of 16 8 O atom = 15.994915 u Mass of neutron = 1.008665 u Mass of hydrogen atom =1.007825 u Q 12. Assuming the splittng of U 235 nucleus liberates 200 MeV energy, find (a) the energy liberated in the fission of 1 kg of U 235 and Page 2 Exercises For JEE Main Subjective Questions Note You can take approximations in the answers. Radioactivity Q 1. The disintegration rate of a certain radioactive sample at any instant is 4750 disintegrations per minute. Five minutes later the rate becomes 2700 per minute. Calculate (a) decay constant and (b) half-life of the sample Q 2. A radioactive sample contains l.00 × 10 15 atoms and has an activity of 6.00 × 10 11 Bq. What is its half-life? Q 3. Obtain the amount of 60 Co necessary to provide a radioactive source of 8.0 Ci strength. The half-life of 60 Co is 5.3 years? Q 4. The half-life of 238 92 U against alpha decay is 4.5 × 10 9 year. How much disintegration per second occurs in 1 g of 238 92 U ? Q 5. What is the probability that a radioactive atom having a mean life of 10 days decays during the fifth day? Q 6. In an ore containing Uranium, the ratio of 238 Uto 206 Pb nuclei is 3. Calculate the age of the ore, assuming that all the lead present in the ore is the final stable product of 238 U. Take the half-life of 238 U to be 4.5 × 10 9 years. Q 7. The half-lives of radioisotopes P 32 and P 33 are 14 days and 25 days respectively. These radioisotopes are mixed in the ratio of 4 :1 of their atoms. If the initial activity of the mixed sample is 3.0 m Ci, find the activity of the mixed isotopes after 60 year. Nuclear Reactions Q 8. Complete the following reactions. (a) 226 88 Ra ? ? ? (b) 19 19 89 OF ?? (c) 25 25 13 12 AI Mg ?? Q 9. Consider two decay reactions. (a) 236 206 92 82 U Pb ?? 10 protons + 20 neutrons (b) 236 206 4 92 82 2 U Pb 8 He ? ? ? 6 electrons Are both the reactions possible? Q 10. Obtain the binding energy of a nitrogen nucleus from the following data : m H = 1.00783 u, m N = 1.00867 u, 14 7 m( N) = 14.00307 u Give your answer in units of MeV. [Remember 1 u = 931.5 Me V/c 2 ] Q 11. 8 protons and 8 neutrons are separately at rest. How much energy will be released if we form 16 8 O nucleus? Given: Mass of 16 8 O atom = 15.994915 u Mass of neutron = 1.008665 u Mass of hydrogen atom =1.007825 u Q 12. Assuming the splittng of U 235 nucleus liberates 200 MeV energy, find (a) the energy liberated in the fission of 1 kg of U 235 and (b) the mass of the coal with calorific value of 30 kJ/g which is equivalent to 1 kg of U 235 . Q 13. 212 83 Bi decays as per following equation. 212 208 4 83 82 2 Bi TI He ?? The kinetic energy of ?-particle emitted is 6.802 MeV. Calculate the kinetic energy of TI recoil atoms. Q 14. In a neutron induced fission of 92U 235 nucleus, usable energy of 185 MeV is released. If 92U 235 reactor is continuously operating it at a power level of 100 MW how long will it take for 1 kg of uranium to be consumed in this reactor? Q 15. Calculate the Q-values of the following fusion reactions : (a) 2 2 3 1 1 1 1 1 H H H H ? ? ? (b) 2 2 3 1 1 2 H H He n ? ? ? (c) 2 3 4 1 1 2 H H He n ? ? ? Atomic masses are 2 1 m( H) = 2.014102u, 3 1 m( H) = 3.016049u, 3 2 m( He) = 3.016029 u, 4 2 m( He) = 4.002603 u, 1 1 m( H) = 1.007825 U Q 16. Calculate the Q-value of the fusion reaction 4 He + 4 He ? 8 Be Is such a fusion energetically favourable? Atomic mass of 8 Be is 8.0053 u and that of 4 He is 4.0026 u. Solutions 1. (a) R = R0e - ?t R = 2700 per minute, R0 = 4750 per minute t = 5 minute Find ?. (b) 2. R = ?N 6 × 10 11 =1.0 × l0 15 ? ? = 6 × 10 -4 s = 1155 s= 19.25 min 3. R = ?N = 7.14 × 10 19 × 60gm = 7.11× 10 -3 gm 4. = 1.23 x 10 4 dps 5. = 10days Page 3 Exercises For JEE Main Subjective Questions Note You can take approximations in the answers. Radioactivity Q 1. The disintegration rate of a certain radioactive sample at any instant is 4750 disintegrations per minute. Five minutes later the rate becomes 2700 per minute. Calculate (a) decay constant and (b) half-life of the sample Q 2. A radioactive sample contains l.00 × 10 15 atoms and has an activity of 6.00 × 10 11 Bq. What is its half-life? Q 3. Obtain the amount of 60 Co necessary to provide a radioactive source of 8.0 Ci strength. The half-life of 60 Co is 5.3 years? Q 4. The half-life of 238 92 U against alpha decay is 4.5 × 10 9 year. How much disintegration per second occurs in 1 g of 238 92 U ? Q 5. What is the probability that a radioactive atom having a mean life of 10 days decays during the fifth day? Q 6. In an ore containing Uranium, the ratio of 238 Uto 206 Pb nuclei is 3. Calculate the age of the ore, assuming that all the lead present in the ore is the final stable product of 238 U. Take the half-life of 238 U to be 4.5 × 10 9 years. Q 7. The half-lives of radioisotopes P 32 and P 33 are 14 days and 25 days respectively. These radioisotopes are mixed in the ratio of 4 :1 of their atoms. If the initial activity of the mixed sample is 3.0 m Ci, find the activity of the mixed isotopes after 60 year. Nuclear Reactions Q 8. Complete the following reactions. (a) 226 88 Ra ? ? ? (b) 19 19 89 OF ?? (c) 25 25 13 12 AI Mg ?? Q 9. Consider two decay reactions. (a) 236 206 92 82 U Pb ?? 10 protons + 20 neutrons (b) 236 206 4 92 82 2 U Pb 8 He ? ? ? 6 electrons Are both the reactions possible? Q 10. Obtain the binding energy of a nitrogen nucleus from the following data : m H = 1.00783 u, m N = 1.00867 u, 14 7 m( N) = 14.00307 u Give your answer in units of MeV. [Remember 1 u = 931.5 Me V/c 2 ] Q 11. 8 protons and 8 neutrons are separately at rest. How much energy will be released if we form 16 8 O nucleus? Given: Mass of 16 8 O atom = 15.994915 u Mass of neutron = 1.008665 u Mass of hydrogen atom =1.007825 u Q 12. Assuming the splittng of U 235 nucleus liberates 200 MeV energy, find (a) the energy liberated in the fission of 1 kg of U 235 and (b) the mass of the coal with calorific value of 30 kJ/g which is equivalent to 1 kg of U 235 . Q 13. 212 83 Bi decays as per following equation. 212 208 4 83 82 2 Bi TI He ?? The kinetic energy of ?-particle emitted is 6.802 MeV. Calculate the kinetic energy of TI recoil atoms. Q 14. In a neutron induced fission of 92U 235 nucleus, usable energy of 185 MeV is released. If 92U 235 reactor is continuously operating it at a power level of 100 MW how long will it take for 1 kg of uranium to be consumed in this reactor? Q 15. Calculate the Q-values of the following fusion reactions : (a) 2 2 3 1 1 1 1 1 H H H H ? ? ? (b) 2 2 3 1 1 2 H H He n ? ? ? (c) 2 3 4 1 1 2 H H He n ? ? ? Atomic masses are 2 1 m( H) = 2.014102u, 3 1 m( H) = 3.016049u, 3 2 m( He) = 3.016029 u, 4 2 m( He) = 4.002603 u, 1 1 m( H) = 1.007825 U Q 16. Calculate the Q-value of the fusion reaction 4 He + 4 He ? 8 Be Is such a fusion energetically favourable? Atomic mass of 8 Be is 8.0053 u and that of 4 He is 4.0026 u. Solutions 1. (a) R = R0e - ?t R = 2700 per minute, R0 = 4750 per minute t = 5 minute Find ?. (b) 2. R = ?N 6 × 10 11 =1.0 × l0 15 ? ? = 6 × 10 -4 s = 1155 s= 19.25 min 3. R = ?N = 7.14 × 10 19 × 60gm = 7.11× 10 -3 gm 4. = 1.23 x 10 4 dps 5. = 10days ? ? = 0.1 day -1 Probability of decay = 1 â€“ e - ?t = 1 - e- 0.1×5 = 0.39 6. N0 = 3 + 1 = 4 N =3 From Eqs. (i) and (ii), we get t = 1.88 × 10 9 yr 7. (T= half life) R01 + R02 = 8MCi (is given) From here we can find No. After t = 60 yr 8. See the answer. 9. (a) 82 + 10 = 92, 206 + 10 + 20 = 236 So this reaction is possible. (b) 82 + 16 - 6 = 92, 206 + 32 = 238 But antineutrino is also emitted with ? ~1 (or electron) decay. 10. Binding energy = ?m × 931.5 MeV = (7 × 1.00783 + 7 × 1.00867-14.00307) 931.5 = 104.72 MeV 11. Energy released = binding energy ?m × 931.5MeV (8 × 1.007825 + 8 × 1.008665 - 15.994915) × 931.5 = 127.62MeV 12. (a) Number of nuclei in 1 kg of U 235 ? Total energy released = (N × 200) MeV (6.02 × 10 26 ) (200) (1.6 × 10 -13 ) = 8.19 × 10 13 J (b) = 2.73 × 10 9 gm = 2.73 × 10 6 kg 13. Form momentum conservation, Page 4 Exercises For JEE Main Subjective Questions Note You can take approximations in the answers. Radioactivity Q 1. The disintegration rate of a certain radioactive sample at any instant is 4750 disintegrations per minute. Five minutes later the rate becomes 2700 per minute. Calculate (a) decay constant and (b) half-life of the sample Q 2. A radioactive sample contains l.00 × 10 15 atoms and has an activity of 6.00 × 10 11 Bq. What is its half-life? Q 3. Obtain the amount of 60 Co necessary to provide a radioactive source of 8.0 Ci strength. The half-life of 60 Co is 5.3 years? Q 4. The half-life of 238 92 U against alpha decay is 4.5 × 10 9 year. How much disintegration per second occurs in 1 g of 238 92 U ? Q 5. What is the probability that a radioactive atom having a mean life of 10 days decays during the fifth day? Q 6. In an ore containing Uranium, the ratio of 238 Uto 206 Pb nuclei is 3. Calculate the age of the ore, assuming that all the lead present in the ore is the final stable product of 238 U. Take the half-life of 238 U to be 4.5 × 10 9 years. Q 7. The half-lives of radioisotopes P 32 and P 33 are 14 days and 25 days respectively. These radioisotopes are mixed in the ratio of 4 :1 of their atoms. If the initial activity of the mixed sample is 3.0 m Ci, find the activity of the mixed isotopes after 60 year. Nuclear Reactions Q 8. Complete the following reactions. (a) 226 88 Ra ? ? ? (b) 19 19 89 OF ?? (c) 25 25 13 12 AI Mg ?? Q 9. Consider two decay reactions. (a) 236 206 92 82 U Pb ?? 10 protons + 20 neutrons (b) 236 206 4 92 82 2 U Pb 8 He ? ? ? 6 electrons Are both the reactions possible? Q 10. Obtain the binding energy of a nitrogen nucleus from the following data : m H = 1.00783 u, m N = 1.00867 u, 14 7 m( N) = 14.00307 u Give your answer in units of MeV. [Remember 1 u = 931.5 Me V/c 2 ] Q 11. 8 protons and 8 neutrons are separately at rest. How much energy will be released if we form 16 8 O nucleus? Given: Mass of 16 8 O atom = 15.994915 u Mass of neutron = 1.008665 u Mass of hydrogen atom =1.007825 u Q 12. Assuming the splittng of U 235 nucleus liberates 200 MeV energy, find (a) the energy liberated in the fission of 1 kg of U 235 and (b) the mass of the coal with calorific value of 30 kJ/g which is equivalent to 1 kg of U 235 . Q 13. 212 83 Bi decays as per following equation. 212 208 4 83 82 2 Bi TI He ?? The kinetic energy of ?-particle emitted is 6.802 MeV. Calculate the kinetic energy of TI recoil atoms. Q 14. In a neutron induced fission of 92U 235 nucleus, usable energy of 185 MeV is released. If 92U 235 reactor is continuously operating it at a power level of 100 MW how long will it take for 1 kg of uranium to be consumed in this reactor? Q 15. Calculate the Q-values of the following fusion reactions : (a) 2 2 3 1 1 1 1 1 H H H H ? ? ? (b) 2 2 3 1 1 2 H H He n ? ? ? (c) 2 3 4 1 1 2 H H He n ? ? ? Atomic masses are 2 1 m( H) = 2.014102u, 3 1 m( H) = 3.016049u, 3 2 m( He) = 3.016029 u, 4 2 m( He) = 4.002603 u, 1 1 m( H) = 1.007825 U Q 16. Calculate the Q-value of the fusion reaction 4 He + 4 He ? 8 Be Is such a fusion energetically favourable? Atomic mass of 8 Be is 8.0053 u and that of 4 He is 4.0026 u. Solutions 1. (a) R = R0e - ?t R = 2700 per minute, R0 = 4750 per minute t = 5 minute Find ?. (b) 2. R = ?N 6 × 10 11 =1.0 × l0 15 ? ? = 6 × 10 -4 s = 1155 s= 19.25 min 3. R = ?N = 7.14 × 10 19 × 60gm = 7.11× 10 -3 gm 4. = 1.23 x 10 4 dps 5. = 10days ? ? = 0.1 day -1 Probability of decay = 1 â€“ e - ?t = 1 - e- 0.1×5 = 0.39 6. N0 = 3 + 1 = 4 N =3 From Eqs. (i) and (ii), we get t = 1.88 × 10 9 yr 7. (T= half life) R01 + R02 = 8MCi (is given) From here we can find No. After t = 60 yr 8. See the answer. 9. (a) 82 + 10 = 92, 206 + 10 + 20 = 236 So this reaction is possible. (b) 82 + 16 - 6 = 92, 206 + 32 = 238 But antineutrino is also emitted with ? ~1 (or electron) decay. 10. Binding energy = ?m × 931.5 MeV = (7 × 1.00783 + 7 × 1.00867-14.00307) 931.5 = 104.72 MeV 11. Energy released = binding energy ?m × 931.5MeV (8 × 1.007825 + 8 × 1.008665 - 15.994915) × 931.5 = 127.62MeV 12. (a) Number of nuclei in 1 kg of U 235 ? Total energy released = (N × 200) MeV (6.02 × 10 26 ) (200) (1.6 × 10 -13 ) = 8.19 × 10 13 J (b) = 2.73 × 10 9 gm = 2.73 × 10 6 kg 13. Form momentum conservation, 14. Number of nuclei in 1 kg of uranium, Now, (6.02 × 10 26 ) (185 × 1.6 × 10 -13 ) = (100 × l0 6 )t t = 7.58 × 10 5 s = 8.78days 15. Q-value = ( ?m) (931.5) MeV (a) Q-value = (2 × 2.014102 - 3.016049 - 1.007825) × 931.5 = 4.05 MeV Similarly Q-value of other parts can also be obtained. 16. Q-value = ( ?m) × 931.5 MeV = (2 × 4.0026 - 8.0053) × 931.5 = -0.0931 MeV = - 93.1 keV Objective Questions Single Correct Option Q 1. During a beta decay (a) an atomic electron is ejected (b) an electron present inside the nucleus is ejected (c) a neutron in the nucleus decays emitting an electron (d) a part of the binding energy is converted into electron Q 2. In the nucleus of helium if Fl is the net force between two protons, F2 is the net force between two neutrons and F3 is the net force between a proton and a neutron. Then (a) F1 = F2 = F3 (b) F1 > F2 > F3 (c) F2 > F3 > F1 (d) F2 = F3 > F1 Q 3. What are the respective number of ? and ?-particles emitted in the following radioactive decay? 200 168 90 80 XY ? (a) 6 and 8 (b) 6 and 6 (c) 8 and 8 (d) 8 and 6 Q 4. If an atom of 235 92 U , after absorbing a slow neutron, undergoes fission to form an atom of 138 54 Xe and an atom of 94 38 Sr , the other particles produced are (a) one proton and two neutrons (b) three neutrons (c) two neutrons (d) one proton and one neutron Q 5. Nucleus A is converted into C through the following reactions A ? B + ? B ? C + 2 ? then Page 5 Exercises For JEE Main Subjective Questions Note You can take approximations in the answers. Radioactivity Q 1. The disintegration rate of a certain radioactive sample at any instant is 4750 disintegrations per minute. Five minutes later the rate becomes 2700 per minute. Calculate (a) decay constant and (b) half-life of the sample Q 2. A radioactive sample contains l.00 × 10 15 atoms and has an activity of 6.00 × 10 11 Bq. What is its half-life? Q 3. Obtain the amount of 60 Co necessary to provide a radioactive source of 8.0 Ci strength. The half-life of 60 Co is 5.3 years? Q 4. The half-life of 238 92 U against alpha decay is 4.5 × 10 9 year. How much disintegration per second occurs in 1 g of 238 92 U ? Q 5. What is the probability that a radioactive atom having a mean life of 10 days decays during the fifth day? Q 6. In an ore containing Uranium, the ratio of 238 Uto 206 Pb nuclei is 3. Calculate the age of the ore, assuming that all the lead present in the ore is the final stable product of 238 U. Take the half-life of 238 U to be 4.5 × 10 9 years. Q 7. The half-lives of radioisotopes P 32 and P 33 are 14 days and 25 days respectively. These radioisotopes are mixed in the ratio of 4 :1 of their atoms. If the initial activity of the mixed sample is 3.0 m Ci, find the activity of the mixed isotopes after 60 year. Nuclear Reactions Q 8. Complete the following reactions. (a) 226 88 Ra ? ? ? (b) 19 19 89 OF ?? (c) 25 25 13 12 AI Mg ?? Q 9. Consider two decay reactions. (a) 236 206 92 82 U Pb ?? 10 protons + 20 neutrons (b) 236 206 4 92 82 2 U Pb 8 He ? ? ? 6 electrons Are both the reactions possible? Q 10. Obtain the binding energy of a nitrogen nucleus from the following data : m H = 1.00783 u, m N = 1.00867 u, 14 7 m( N) = 14.00307 u Give your answer in units of MeV. [Remember 1 u = 931.5 Me V/c 2 ] Q 11. 8 protons and 8 neutrons are separately at rest. How much energy will be released if we form 16 8 O nucleus? Given: Mass of 16 8 O atom = 15.994915 u Mass of neutron = 1.008665 u Mass of hydrogen atom =1.007825 u Q 12. Assuming the splittng of U 235 nucleus liberates 200 MeV energy, find (a) the energy liberated in the fission of 1 kg of U 235 and (b) the mass of the coal with calorific value of 30 kJ/g which is equivalent to 1 kg of U 235 . Q 13. 212 83 Bi decays as per following equation. 212 208 4 83 82 2 Bi TI He ?? The kinetic energy of ?-particle emitted is 6.802 MeV. Calculate the kinetic energy of TI recoil atoms. Q 14. In a neutron induced fission of 92U 235 nucleus, usable energy of 185 MeV is released. If 92U 235 reactor is continuously operating it at a power level of 100 MW how long will it take for 1 kg of uranium to be consumed in this reactor? Q 15. Calculate the Q-values of the following fusion reactions : (a) 2 2 3 1 1 1 1 1 H H H H ? ? ? (b) 2 2 3 1 1 2 H H He n ? ? ? (c) 2 3 4 1 1 2 H H He n ? ? ? Atomic masses are 2 1 m( H) = 2.014102u, 3 1 m( H) = 3.016049u, 3 2 m( He) = 3.016029 u, 4 2 m( He) = 4.002603 u, 1 1 m( H) = 1.007825 U Q 16. Calculate the Q-value of the fusion reaction 4 He + 4 He ? 8 Be Is such a fusion energetically favourable? Atomic mass of 8 Be is 8.0053 u and that of 4 He is 4.0026 u. Solutions 1. (a) R = R0e - ?t R = 2700 per minute, R0 = 4750 per minute t = 5 minute Find ?. (b) 2. R = ?N 6 × 10 11 =1.0 × l0 15 ? ? = 6 × 10 -4 s = 1155 s= 19.25 min 3. R = ?N = 7.14 × 10 19 × 60gm = 7.11× 10 -3 gm 4. = 1.23 x 10 4 dps 5. = 10days ? ? = 0.1 day -1 Probability of decay = 1 â€“ e - ?t = 1 - e- 0.1×5 = 0.39 6. N0 = 3 + 1 = 4 N =3 From Eqs. (i) and (ii), we get t = 1.88 × 10 9 yr 7. (T= half life) R01 + R02 = 8MCi (is given) From here we can find No. After t = 60 yr 8. See the answer. 9. (a) 82 + 10 = 92, 206 + 10 + 20 = 236 So this reaction is possible. (b) 82 + 16 - 6 = 92, 206 + 32 = 238 But antineutrino is also emitted with ? ~1 (or electron) decay. 10. Binding energy = ?m × 931.5 MeV = (7 × 1.00783 + 7 × 1.00867-14.00307) 931.5 = 104.72 MeV 11. Energy released = binding energy ?m × 931.5MeV (8 × 1.007825 + 8 × 1.008665 - 15.994915) × 931.5 = 127.62MeV 12. (a) Number of nuclei in 1 kg of U 235 ? Total energy released = (N × 200) MeV (6.02 × 10 26 ) (200) (1.6 × 10 -13 ) = 8.19 × 10 13 J (b) = 2.73 × 10 9 gm = 2.73 × 10 6 kg 13. Form momentum conservation, 14. Number of nuclei in 1 kg of uranium, Now, (6.02 × 10 26 ) (185 × 1.6 × 10 -13 ) = (100 × l0 6 )t t = 7.58 × 10 5 s = 8.78days 15. Q-value = ( ?m) (931.5) MeV (a) Q-value = (2 × 2.014102 - 3.016049 - 1.007825) × 931.5 = 4.05 MeV Similarly Q-value of other parts can also be obtained. 16. Q-value = ( ?m) × 931.5 MeV = (2 × 4.0026 - 8.0053) × 931.5 = -0.0931 MeV = - 93.1 keV Objective Questions Single Correct Option Q 1. During a beta decay (a) an atomic electron is ejected (b) an electron present inside the nucleus is ejected (c) a neutron in the nucleus decays emitting an electron (d) a part of the binding energy is converted into electron Q 2. In the nucleus of helium if Fl is the net force between two protons, F2 is the net force between two neutrons and F3 is the net force between a proton and a neutron. Then (a) F1 = F2 = F3 (b) F1 > F2 > F3 (c) F2 > F3 > F1 (d) F2 = F3 > F1 Q 3. What are the respective number of ? and ?-particles emitted in the following radioactive decay? 200 168 90 80 XY ? (a) 6 and 8 (b) 6 and 6 (c) 8 and 8 (d) 8 and 6 Q 4. If an atom of 235 92 U , after absorbing a slow neutron, undergoes fission to form an atom of 138 54 Xe and an atom of 94 38 Sr , the other particles produced are (a) one proton and two neutrons (b) three neutrons (c) two neutrons (d) one proton and one neutron Q 5. Nucleus A is converted into C through the following reactions A ? B + ? B ? C + 2 ? then (a) A and B are isotopes (b) A and C are isobars (c) A and B are isobars (d) A and C are isotopes Q 6. The binding energy of ?-particle is (if mp =1.00785u, mn = 1.00866 u and m ? = 4.00274u) (a) 56.42 MeV (b) 2.821 MeV (c) 28.21 MeV (d) 32.4 MeV Q 7. 7/8 th of the active nuclei present in a radioactive sample has decayed in 8 s. The half life of the sample is (a) 2 s (b) 1 s (c) 7 s (d) 8 s 3 Q 8. A radioactive element disintegrates for a time interval equal to its mean life. The fraction that has disintegrated is (a) 1 e (b) 1 1 e ? (c) 0.693 e (d) 1 0.693 1 e ?? ? ?? ?? Q 9. Starting with a sample of pure 66 3 Cu, 4 ?? ?? ?? of it decays into Zn in 15 minutes. The corresponding half-life is (a) 5 minutes (b) 7.5 minutes (c) 10 minutes (d) 3.5 minutes Q 10. A sample of radioactive substance loses half of its activity in 4 days. The time in which its activity is reduced to 5% is (a) 12 days (b) 8.3 days (c) 17.3 days (d) None of these Q 11. On bombardment of U 235 by slow neutrons, 200 MeV energy is released. If the power output of atomic reactor is 1.6 MW, then the rate of fission will be (a) 5 × 10 16 per second (b) 10 × 10 16 per second (c) 15 × 10 16 per second (d) 20 × 10 16 per second Q 12. Atomic masses of two heavy atoms are A 1 and A 2- Ratio of their respective nuclear densitities will be approximately (a) 1 2 A A (b) 1/3 1 2 A A ?? ?? ?? (c) 1/3 2 1 A A ?? ?? ?? (d) 1 Q 13. A radioactive element is disintegrating having half-life 6.93 s. The fractional change in number of nuclei of the radioactive element during 10 s is (a) 0.37 (b) 0.63 (c) 0.25 (d) 0.50 Q 14. The activity of a radioactive sample goes down to about 6% in a time of 2 hour. The half-life of the sample in minute is about (a) 30 (b) 15 (c) 60 (d) 120 Q 15. What is the probability of a radioactive nucleus to survive one mean life? (a) 1 e (b) 1 e1 ? (c) 1 1 e ? (d) 1 1 e ? AnswersRead More

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