Nuclei PYQs Set 3 (PDF)

Set 3 of 8 · Questions 61-90 of 240

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Mere Teacher · Previous Year Questions JEE Main Physics · Nuclei · Set 3 (Q61-90)
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61. $A radioactive nucleus decays by two different processes. The halflife for the first process is 10 s and that for the second is 100 s . The effective half life of the nucleus is close to$ (1) $12 sec$ (2) $9 sec$ (3) $55 sec$ (4) $6 sec$ 62. $Which of the following is emitted, when_{94}^{239} Pu decays into_{92}^{235} U ?$ (1) $Gamma ray$ (2) $Neutron$ (3) $Electron$ (4) $Alpha particle$ 63. $The radius and mass number of nucleus ' 1 ' is R_{1} and A_{1} respectively. The radius and mass number of nurleus ' 2 ' is R_{2} and A_{2} respectively. If A_{2} is larger than A_{1} by 2 %, then R_{2} is larger than R_{1} by$ (1) $\frac{2}{3} %$ (2) $1 %$ (3) $8 %$ (4) $\frac{3}{2} %$ 64. $The half-life of Au^{198} is 2.7 days. The activity of 1.50 mg of Au^{198} if its atomic weight is 198 g mol^{- 1} is, (N_{A} = 6 \times 10^{23} / mol)$ (1) $240 Ci$ (2) $357 Ci$ (3) $535 Ci$ (4) $252 Ci$ 65. $A radioisotope X with a halflife 1.4 \times 1 0^{9} years decays to Y which is stable. A sample of the rock from a cave was found to contain X and Y in the ratio 1 : 7. The age of the rock is$ (1) $1.96 \times 1 0^{9} years$ (2) $3.92 \times 1 0^{9} years$ (3) $4.20 \times 1 0^{9} years$ (4) $8.40 \times 1 0^{9} years$ 66. $The mass of a_{3}^{7} Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of_{3}^{7} Li nucleus is nearly$ (1) $46 MeV$ (2) $5.6 MeV$ (3) $3.9 MeV$ (4) $23 MeV$ 67. $The masses of two radioactive substances are same and their half lives are 1 year and 2 years respectively. The ratio of their activities after 6 years will be$ (1) $1 : 3$ (2) $1 : 6$ (3) $1 : 4$ (4) $1 : 2$ 68. $A certain mass of Hydrogen is changed to Helium by the process of fusion. The mass defect in fusion reaction is 0.02866 u . The energy liberated per u is (given 1 u = 931 MeV)$ (1) $6.675 MeV$ (2) $13.35 MeV$ (3) $2.67 MeV$ (4) $26.7 MeV$ 69. $The energy equivalent to a mass of 1 kg is$ (1) $9 \times 10^{13} J$ (2) $9 \times 10^{9} J$ (3) $9 \times 10^{16} J$ (4) $9 \times 10^{6} J$ 70. $The half life of a radioactive substance is 20 minutes. The time taken between 50 % decay and 87.5 % decay of the substance will be$ (1) $40 minutes$ (2) $10 minutes$ (3) $30 minutes$ (4) $25 minutes$ 71. $The radius of the first permitted Bohr orbit, for the electron, in a hydrogen atom equals 0.51Å and its ground state energy equals -13.6 eV. If the electron in the hydrogen atom is replaced by muon (μ^{-}) [charge same as electron and mass 207 m_{e}], the first Bohr radius and ground state energy will be$ (1) $0.53 \times 10^{- 13} m, - 3.6 eV$ (2) $25.6 \times 10^{- 13} m, - 2.8 eV$ (3) $2.56 \times 10^{- 13} m, - 2.8 keV$ (4) $2.56 \times 10^{- 13} m, - 13.6 eV$ 72. $In a nuclear reactor, the main purpose of the moderator is to$ (1) $initiate that fission process by giving away its neutron$ (2) $slow down the fast neutrons$ (3) $cool down the excess of heat generated in the reactor$ (4) $absorb excess of neutrons and control the reaction rate$ 73. $A nucleus of mass M emits γ -ray photon of frequency 'v' The loss of internal energy by the nucleus is: [Take 'c' as the speed of electromagnetic wave]$ (1) $hc$ (2) $0$ (3) $hv (1 - \frac{hv}{2 M c ^{2}})$ (4) $hv (1 + \frac{hv}{2 M c ^{2}})$ 74. $The particles emitted in the decay of_{92}^{238} U to_{92}^{234} U$ (1) $2 α and 2β$ (2) $1 α and 2 β$ (3) $1α and 1 β$ (4) $1 α only$ 75. $The half life of radium is about 1600 years. If 100 g of radium existing now, 25 g will remain unchanged after$ (1) $4800 years$ (2) $6400 years$ (3) $2400 years$ (4) $3200 years$ 76. $A nuclear reactor delivers a power of 10^{9} W, the amount of fuel consumed by the reactor in one hour is$ (1) $0.72 g$ (2) $0.04 g$ (3) $0.96 g$ (4) $0.08 g$ 77. $The ratio of magnetic dipole moment of an electron of charge c and mass m in Bohr's orbit in hydrogen atom to its angular momentum is$ (1) $\frac{e}{m}$ (2) $\frac{m}{e}$ (3) $\frac{2 m}{e}$ (4) $\frac{c}{2 m}$ 78. $On bombarding U^{235} by slow neutron, 200 MeV energy is released. If the power output of atomic reactor is 1.6 MW, then the rate of fission will be$ (1) $8 \times 10^{16} / s$ (2) $20 \times 10^{16} / s$ (3) $5 \times 10^{22} / s$ (4) $5 \times 10^{16} / s$ 79. $An element A decays into element C by a two step process A \to B +_{2} He^{4}; B \to C + 2 e^{-}, Then$ (1) $A and C are isotopes$ (2) $A and C are isobars$ (3) $A and B are isotopes$ (4) $A and B are isobars$ 80. $The half-life of_{84}^{209} P_{0} is 103 years. The time it takes fc 100 g sample of_{84}^{209} P_{0} to decay to 3.125 g is$ (1) $3296 years$ (2) $1032 years$ (3) $1648 years$ (4) $515 years$ 81. $A radioactive element forms its own isotope after 3 consecutive disintegrations. The particles emitted are$ (1) $3 β -particles$ (2) $2β-particles and 1 α -particle$ (3) $2β-particles and 1 γ -particle$ (4) $2 α -particles and 1 β -particle.$ 82. $The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an$ (1) $isomer of parent$ (2) $isotone of parent$ (3) $isotope of parent$ (4) $isobar of parent$ 83. $What will be the energy released in joule, in the process of fission by 1 mg of_{92}^{240} U . Assume energy release per fission is 200 MeV . [use Avogadro's number as 6 \times 10^{23} and 1 eV = 1.6 \times (10^{- 19} J)$ (1) $6.2 \times 10^{7} J$ (2) $7.0 \times 10^{7} J$ (3) $8.0 \times 10^{7} J$ (4) $8.2 \times 10^{7} J$ 84. $When an α -particle of mass m moving with velocity v bombards on a heavy nucleus of charge Ze, its distance of closest approach from the nucleus depends on m as [NEET 2016]$ (1) $\frac{1}{m}$ (2) $\frac{1}{m ^{2}}$ (3) $m$ (4) $\frac{1}{m}$ 85. $The half-life of tritium is 12.5 years. What mass of tritium of initial mass 64 mg will remain undecayed after 50 years?$ (1) $32 mg$ (2) $8 mg$ (3) $16 mg$ (4) $4 mg$ 86. $Radiation coming from transitions n = 2 to n = 1 of hydrogen atoms fall on H e^{+} ions in n = 1 and n = 2 states. The possible transition of helium ions as they absorb energy from the radiation is:$ (1) $n = 2 \to n = 3$ (2) $n = 1 \to n = 4$ (3) $n = 2 \to n = 5$ (4) $n = 2 \to n = 4$ 87. $A radioactive sample S_{1} having the activity A_{1} has twice the number of nuclei as another sample S_{2} of activity A_{2} . If A_{2} = 2 A_{1}, then the ratio of half life of S_{1} to the life of S_{2} is$ (1) $4$ (2) $2$ (3) $0.25$ (4) $0.75$ 88. $A radioactive substance of half life 138.6 days is placed in a box. After n days only 20 % of the substance is present then the value of n is [ln (5) = 1.61]$ (1) $693$ (2) $138.6$ (3) $277.2$ (4) $322$ 89. $A radio-active sample of half-life 10 days contains 1000 x nuclei. Number of original nuclei present after 5 days is$ (1) $707 x$ (2) $750 x$ (3) $500 x$ (4) $250 x$ 90. $A radioactive sample has an average life of 30ms and is decaying. A capacitor of capacitance 200 μF is first charged and later connected with resistor ‘R’. If the ratio of charge on capacitor to the activity of radioactive sample is fixed with respect to time then the value of 'R' should be ___Ω .$