JEE Questions for Physics Atoms And Nuclei Quiz 18 - MCQExams.com


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  • 2)
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A radioactive nucleus (initial mass number A and atomic number Z) emits 3 α - particles and 2 positrons. The ratio of number of neutrons to that of protons in the final nucleus will be

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  • 2)
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Which one is correct about fission?
  • Approx. 0.1% mass converts into energy
  • Most of energy of fission is in the form of heat
  • In a fission of U235 about 200 eV energy is released
  • On an average, one neutron is released per fission of U235
Consider a radioactive material of half-life 1.0 minute. If one of the nuclei decays now, the next one will decay
  • After 1 minute
  • 2)
    Physics-Atoms and Nuclei-63415.png

  • Physics-Atoms and Nuclei-63416.png
  • After any time
In which radioactive disintegration, neutron dissociates into proton and electron
  • He+1 emission
  • β - emission
  • γ –emission
  • Positron emission
Select the wrong statement
  • Radioactivity is a statistical process
  • Radioactivity is a spontaneous process
  • Radioactivity is neutral characteristics of few elements
  • Radioactive elements cannot be produced in the laboratory
The relationship between λ and half life (T1/2) of a radioactive substance is

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    Physics-Atoms and Nuclei-63418.png

  • Physics-Atoms and Nuclei-63419.png

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The half life (T) and the disintegration constant (λ) of a radioactive substance are related as
  • λT = 1
  • λT = 0.693

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In the uranium radioactive series, the initial nucleus is 92U238 and the final nucleus is 82Pb206. When the uranium nucleus decays to lead, the number of α - particles emitted will be
  • 1
  • 2
  • 4
  • 8
The half life of 131I is 8 days. Given a sample of 131I at time t = 0, we can assert that
  • No nucleus will decay before t = 4 days
  • No nucleus will decay before t = 8 days
  • All nuclei will decay before t = 16 days
  • A given nucleus may decay at any time after t = 0
Which of the following statements are true regarding radioactivity?
(I) All radioactive elements decay exponentially with time
(II) Half life time of a radioactive element is time required for one half of the radioactive atoms to disintegrate
(III) Age of earth can be determined with the help of radioactive dating
(IV) Half life time of a radioactive element is 50% of its average life period
Select correct answer using the codes given below Codes
  • I and II
  • I, III and IV
  • I, II and III
  • II and III
The particles emitted by radioactive decay are deflected by magnetic field. The particles will be
  • Protons and α - particles
  • Electrons, protons and α - particles
  • Electrons, protons and neutrons
  • Electrons and α - particles
Half life of a radioactive element is 10 days. The time during which quantity remains 1/10 of initial mass will be
  • 100 days
  • 50 days
  • 33 days
  • 16 days

Physics-Atoms and Nuclei-63427.png
  • A = 234, B = 90, C = 234, D = 91, E = β
  • A = 234, B = 90, C = 238, D = 94, E = α
  • A = 238, B = 93, C = 234, D = 91, E = β
  • A = 234, B = 90, C = 234, D = 93, E = α
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
  • 0.230 per minute
  • 0.461 per minute
  • 0.691 per minute
  • 0.922 per minute
Consider the following two statements
A. Energy spectrum of α–particles emitted in radioactive decay is discrete
B. Energy spectrum of β–particles emitted in radioactive decay is continuous
  • Only A is correct
  • Only B is correct
  • A is correct but B is wrong
  • Both A and B are correct
Which one of the following statements is true, if half-life of a radioactive substance is 1 month?

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    Physics-Atoms and Nuclei-63431.png
  • The substance will disintegrate completely in 4 months

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  • The substance will disintegrate completely in 2 months
In beta decay
  • The parent and daughter nuclei have same number of protons
  • The daughter nucleus has one proton less than the parent nucleus
  • The daughter nucleus has one proton more than the parent nucleus
  • The daughter nucleus has one neutron more than the parent nucleus
An observer A sees an asteroid with a radioactive element moving by at a speed = 0.3c and measures the radioactivity decay time to be TA. Another observer B is moving with the asteroid and measures its decay time as TB. Then TA and TB are related as below
  • TB < TA
  • TB = TA
  • TB > TA
  • Either (or (depending on whether the asteroid is approaching or moving away from A.
Three fourth of the active decays in a radioactive sample in 3/4 s. The half life of the sample is

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  • 2)
    Physics-Atoms and Nuclei-63435.png

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1 curie is equal to
  • 3 × 1010 disintegrations/s
  • 3.7 × 107 disintegrations/s
  • 5 × 107 disintegrations/s
  • 3.7 × 1010 disintegrations/s
Half-life is measured by
  • Geiger-Muller counter
  • Carbon dating
  • Spectroscopic method
  • Wilson-Cloud chamber
The decay constant of a radioactive element is 1.5 × 10–9 per second. Its mean life in seconds will be
  • 1.5 × 109
  • 4.62 × 108
  • 6.67 × 108
  • 10.35 × 108
Nucleus produced due to α–decay of the nucleus ZXA is
  • Z+2YA+4
  • ZYA
  • Z-2YA-4
  • Z-4YA-2
Which of the following processes represent a gamma-decay
  • AXZ + γ →AXZ–1 + a + b
  • AXZ + 1n0 → A–3XZ–2 + c
  • AXZ → AXZ + f
  • AXZ + e–1 → AXZ–1 + g
The half-life of 215At is 100µs. The time taken for the radioactivity of a sample of 215At to decay to 1/16th of its initial value is
  • 400 μs
  • 6.3 µs
  • 40 μs
  • 300 μs
A radioactive substance has an average life of 5 hours. In a time of 5 hours
  • Half of the active nuclei decay
  • Less than half of the active nuclei decay
  • More than half of the active nuclei decay
  • All active nuclei decay
A radioactive sample at any instant has its disintegrations rate 5000 disintegrations per minute. After 5 minutes, the rate 1250 disintegrations per minute. Then, the decay constant (per minute) is
  • 0.81n 2
  • 0.41n 2
  • 0.2 ln 2
  • 0.1 ln 2
A count rate meter shows a count of 240 per minute from a given radioactive source. One hour later the meter shows a count rate of 30 per minute. The half-life of the source is
  • 120 min
  • 80 min
  • 30 min
  • 20 min
Activity of radioactive element decreased to one third of original activity R0 in 9 years. After further 9 years, its activity will be
  • R0
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    Physics-Atoms and Nuclei-63445.png

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A nucleus decays by β+ emission followed by a gamma emission. If the atomic and mass numbers of parent nucleus are Z and A respectively, the corresponding numbers for the daughter nucleus are respectively
  • Z – 1 and A – 1
  • Z + 1 and A
  • Z – 1 and A
  • Z + 1 and A – 1
C14 has half life 5700 years. At the end of 11400 years, the actual amount left is
  • 0.5 of original amount
  • 0.25 of original amount
  • 0.125 of original amount
  • 0.0625 of original amount
The half-life period of a radio-active element X is same as the life time of another radio-active element Y. Initially they have the same number of atoms. Then
  • X will decay faster than Y
  • Y will decay faster than X
  • X and Y have same decay rate initially
  • X and Y decay at same rate always
The phenomenon of radioactivity is
  • Exothermic change which increases or decreases with temperature
  • Increases on applied pressure
  • Nuclear process does not depend on external factors
  • None of the above
Consider two nuclei of the same radioactive nuclide. One of the nuclei was created in a supernova explosion 5 billion years ago. The other was created in a nuclear reactor 5 minutes ago. The probability of decay during the next time is
  • Different for each nuclei
  • Nuclei created in explosion decays first
  • Nuclei created in the reactor decays first
  • Independent of the time of creation
For a radioactive nucleus, the mean life is T, If the number of decays per unit time is n at t = 0, the number of decays between time 0 and t, is
  • nTe–t/T
  • n(1 – e–t/T)
  • nT(1 – e–t/T)
  • ne–t/T
What is the disintegration constant of radon, if the number of its atoms diminishes by 18% in 24 h ?
  • 2.1 × 10–3s–1
  • 2.1 × 10–4s–1
  • 2.1 × 10–5s–1
  • 2.1 × 10–6s–1
A radioactive sample has 4 × 1010 nuclei at a certain time. The number of active nuclei still remaining after 4 half lives is
  • 1 × 1010
  • 5 × 109
  • 25 × 108
  • 5 × 108
A common example of β–decay is
15P32 → 16P32 + x + y Then x and y stand for
  • Electron and neutrino
  • Positron and neutrino
  • Electron and antineutrino
  • Positron and antineutrino

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  • 1.33 MeV and 1.17 MeV in succession
  • 1.17 MeV and 1.33 MeV in succession
  • 1.37 MeV and 1.13 MeV in succession
  • 1.13 MeV and 1.37 MeV in succession
  • 1.17 MeV and 1.13 MeV in succession
The half-life of a radioactive substance is 20 minutes. The approximate time interval (t2 – t1) between the time t2 when 2/3 of it has decayed and time t1 when 1/3 of it had decayed is
  • 7 min
  • 14 min
  • 20 min
  • 28 min
Neutrons are used in nuclear fission, because
  • Neutrons are attracted by nucleus
  • Mass of neutrons is greater than protons
  • Neutrons are neutral and hence are not repelled by the nucleus
  • Neutrons could be accelerated to a greater energy
Mean life of neutron is about
  • 100 seconds
  • 1000 seconds
  • 10 seconds
  • 1 seconds
In hydrogen atom, electron makes transition from n = 4 to n =1 level. Recoil momentum of the H atom will be
  • 3.4 × 10–27 N–s
  • 6.8 × 10–27 N–s
  • 3.4 × 10–24 N–s
  • 6.8 × 10–24 N–s
A sodium atom is in one of the states labeled \'Lowest excited levels\'. It remains in that state for an average time of 10-8 s, before to makes a transition back to a ground state. What is the uncertainty in energy of that excited state ?
  • 6.56 × 10–8 eV
  • 2 × 10–8 eV
  • 10–8 eV
  • 8 × 10–8 eV
A hydrogen atom in its ground state absorbs 10.2 eV of energy. The orbital angular momentum is increased by
(Given Planck\'s constant h = 6.6 × 10–34 J–s)
  • 1.05 × 10–34 J–s
  • 3.16 × 10–34 J–s
  • 2.11 × 10–34 J–s
  • 4.22 × 10–34 J–s
Imagine an atom made up of a proton and a hypothetical particle of double the mass of the electron but having the same charge as the electron. Apply the Bohr\'s atom model and consider all possible transitions of this hypothetical particle to the first excited level. The longest wavelength photon that will be emitted has wavelength λ (given is terms of the Rydberg constant R for the hydrogen atom) is equal to
  • 9/(5R)
  • 36/ (5R)
  • 18/ (5R)
  • 4/R
A Hydrogen atom and a Li++ ion are both in the second excited state. If lH and lLi are their respective electronic angular momenta, and EH and ELi their respective energies, then
  • lH > lLi and | EH | > | ELi |
  • lH = lLi and | EH | < | ELi |
  • lH = lLi and | EH | > | ELi |
  • lH < lLi and | EH | < | ELi |

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  • The attraction between the electron and the nucleus is different in the two cases
  • The size of the two nuclei are different
  • The nuclear forces are different in the two cases
  • The masses of the two nuclei are different
A star initially has 1040 deuterons. It produces energy via the processes
1H2 + 1H2 → 1H3 + P
1H2 + 1H3 → 2He4 + n
The masses of the nuclei are as follows M (H2) = 2.014 amu; M (p) = 1.007 amu; M (n) =1.008 amu; M(He4) = 4.001 amu
If the average power radiated by the star is 1016 W, the deuteron supply of the star is exhausted in a time of the order of
  • 106 s
  • 108 s
  • 1012 s
  • 1016 s
0:0:1


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