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NCERT Solutions for class 12 Physics | Chapter 13 - Nuclei

(1) The Bohr model of atoms
[A] assumes that the angular momentum of elec-trons is quantized.
[B] uses Einstein’s photoelectric equation.
[C] predicts continuous emission spectra for at-oms.
[D] predicts the same emission spectra for all types of atoms.
Answer: assumes that the angular momentum of elec-trons is quantized.
(2) According to Yukawa’s theory of nuclear forces, the origin of nuclear force between nucleons is due to the exchange of
[A] mesons
[B] photons
[C] electrons
[D] positrons
Answer: photons

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(3) During negative β-decay, an antineutrino is also emitted along with the emitted electron. Then,
[A] only linear momentum will be conserved
[B] total linear momentum and total angular momentum but not total energy will be conserved
[C] total linear momentum, and total energy but not total angular momentum will conserved
[D] total linear momentum, total angular momentum and total energy will be conserved
Answer: total linear momentum, total angular momentum and total energy will be conserved
(4) Consider α and β particles and γ-rays each having an energy of 0.5 MeV. In the increasing order of penetrating power, the radiation are respectively
[A] α, β, γ
[B] α, γ, β
[C] β, γ, α
[D] γ β, α
Answer: α, β, γ
(5) 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
[A] isomer of parent
[B] isotone of parent
[C] isotope of parent
[D] isobar of parent
Answer: isotope of parent
(6) The radius of a spherical nucleus as measured by electron scattering is 3.6 fm. What is the mass number of the nucleus most likely to be?
[A] 27
[B] 40
[C] 56
[D] 120
Answer: 27
(7) In nuclear reactors, the control rods are made of
[A] cadmium
[B] graphite
[C] krypton
[D] plutonium
Answer: cadmium
(8) The half life of a radioactive susbtance is 30 days. What is the time taken to disintegrate to 3/4th of its original mass?
[A] 30 days
[B] 15 days
[C] 60 days
[D] 90 days
Answer: 60 days
(9) Order of magnitude of density of uranium nucleus is
[A] 1020 kg m-3
[B] 1017 kg m-3
[C] 1014 kg m-3
[D] 1011 kg m-3
Answer: 1011 kg m-3
(10) An electron emitted in beta radiation originates from
[A] inner orbits of atom
[B] free electrons existing in the nuclei
[C] decay of a neutron in a nuclei
[D] photon escaping from the nucleus
Answer: decay of a neutron in a nuclei
(11) The mass number of iron nucleus is 56 the nuclear density is
[A] 2.29 × 1016 kg m-3
[B] 2.29 × 1017 kg m-3
[C] 2.29 × 1018 kg m-3
[D] 2.29 × 1015 kg m-3
Answer: 2.29 × 1017 kg m-3
(12) The equation 41 1H+ → 24He2+ + 2e + 26 MeV represents
[A] β-decay
[B] γ-decay
[C] fusion
[D] fission
Answer: fusion
(13) An element A decays into an element C by a two step process A → B+ 2He4 and B → C + 2e. Then,
[A] A and C are isotopes
[B] A and C are isobars
[C] B and C are isotopes
[D] A and B are isobars
Answer: A and C are isotopes
(14) Complete the series 6He → e + 6Li +
[A] neutrino
[B] antineutrino
[C] proton
[D] neutron
Answer: antineutrino
(15) Light energy emitted by star is due to
[A] breaking of nuclei
[B] joining of nuclei
[C] burning of nuclei
[D] reflection of solar light
Answer: joining of nuclei
(16) In nuclear reaction, there is conservation of
[A] mass only
[B] energy only
[C] momentum only
[D] mass, energy and momentum
Answer: mass, energy and momentum
(17) Alpha particle emitted from a radioactive material are:
[A] Helium nuclei
[B] Hydrogen nuclei
[C] Lithium nuclei
[D] None of the above
Answer: Helium nuclei
(18) An electron and a positron each having a mass equivalent to 0.53 MeV annihilate each other and produce a photon. The minimum energy of the photon is.
[A] 0.53 MeV
[B] 1.06 MeV
[C] 2.12 MeV
[D] zero
Answer: 1.06 MeV
(19) Rutherford is the unit of:
[A] radioactivity
[B] energy
[C] photoelectric current
[D] magnetic field
Answer: radioactivity
(20) When the mass of a sample of a radioactive substance decreases, the mean life of the sample:
[A] increases
[B] decreases
[C] remain unchanged
[D] first decreases then increases
Answer: remain unchanged

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