NCERT Solutions for class 12 Physics | Chapter 13 - Nuclei

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Questions
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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