Class 12 Nuclei CBSE Questions & Answers

Class 12 · Nuclei

This is Physics Class 12 Nuclei CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
In a nuclear reaction which of the following is conserved
  • A
    Momentum only
  • B
    Charge only
  • C
    All the above
    Correct
  • D
    Sum of mass and energy only
2
The end product of the decay of \(_{{\rm{9}}0}{\rm{T}}{{\rm{h}}^{{\rm{232}}}}{\rm{i}}{{\rm{s}}_{{\rm{82}}}}{\rm{P}}{{\rm{b}}^{{\rm{2}}0{\rm{8}}}}\).The number of alpha and beta particles emitted are
  • A
    3, 3
  • B
    6, 4
    Correct
  • C
    4, 6
  • D
    6, 0
3
If 10\(\% \) of a substance decays in 10 days, then approximate percentage of substance left after 24 days is
  • A
    70
  • B
    78.0
    Correct
  • C
    75
  • D
    80
4
Half life of a substance is 20 minutes. What is the time between 33\(\% \) decay and 67 \(\% \) decay?
  • A
    30 minutes
  • B
    25 minutes
  • C
    20 minutes
    Correct
  • D
    40 minutes
5
At a given time there are 25\(\% \) undecayed nuclei in a sample. After 10 seconds number of undecayed nuclei reduces to 12.5\(\% \). Then mean life of the nuclei will be about
  • A
    10 sec
  • B
    12 sec
  • C
    22 sec
  • D
    15 sec
    Correct
6
90\(\% \) of a radioactive sample is left undisintegrated after time τ has elapsed, what percentage of initial sample will decay in a total time\({\rm{2}}\tau \)?
  • A
    38\(\% \)
  • B
    62\(\% \)
  • C
    9\(\% \)
  • D
    19\(\% \)
    Correct
7
A radio-active element has half life of 15 yrs. What is the fraction that will decay in 30 yrs?.
  • A
    0.25
  • B
    0.85
  • C
    0.75
    Correct
  • D
    0.50
8
A radioactive material decays by simultaneous emission of two particles with respective half lives 1620 and 810 years. The time in years, after which one fourth of the material remains is
  • A
    1080.0
    Correct
  • B
    4860
  • C
    2340
  • D
    3240
9
Which of the following radiations has the least wave length?
  • A
    \(\chi \) –rays
  • B
    \(\beta \) –rays
  • C
    \(\alpha \) –rays
  • D
    \(\gamma \) –rays
    Correct
10
As the mass number A increases, which of the following quantities related to a nucleus does not change?
  • A
    binding energy
  • B
    volume
  • C
    density
    Correct
  • D
    mass
11
In which of the following decays does the element not change?
  • A
    \(\beta + \)-decay
  • B
    \(\beta -\)-decay
  • C
    \(\gamma \) –decay
    Correct
  • D
    \(\alpha \) –decay
12
In any nuclear reaction the reactants and the resultants must always be in conformity with the law of conservation of
  • A
    both charge and mass number
    Correct
  • B
    mass number alone
  • C
    charge number alone
  • D
    energy alone
13
Choose the WRONG statement.
  • A
    The nuclear force becomes very strong if the nucleus contains a large number of nucleons
    Correct
  • B
    Nuclei with atomic number greater than 82 show a tendency to disintegrate.
  • C
    The nuclear force becomes weak if the nucleus contains too many protons compared to the number of neutrons
  • D
    The nuclear force becomes weak if the nucleus contains too many neutrons compared to the number of protons
14
What is particle \(\chi \) in the following nuclear reaction?, \({}_4^9Be + {}_2^4He \to {}_6^{12}C + \chi \)
  • A
    Neutron
    Correct
  • B
    Proton
  • C
    Photon
  • D
    Electron
15
Graphite and heavy water are two common moderators used in a nuclear reactor. The function of the moderator is
  • A
    to control the energy released in the reactor
  • B
    to cool the reactor
  • C
    to slow down the neutrons to thermal energies
    Correct
  • D
    to absorb the neutrons and stop the chain reaction