Class 12 Physics Nuclei (MCQ)

Q.1. For a nuclear fusion process, suitable nuclei are
(a) any nuclei
(b) heavy nuclei
(c) lighter nuclei
(d) nuclei lying in the middle of periodic table

Answer Answer: (c)

Q.2. In the uranium radioactive series, the initial nucleus is 92U238 and that the final nucleus is 82Pb206. When uranium nucleus decays to lead, the number of α particles and β particles
emitted are
(a) 8α, 6β
(b) 6α, 7β
(c) 6α, 8β
(d) 4α, 3β

Answer Answer: (a)

Q.3. The nuclear radius is of the order of
(a) 10–10 m
(b) 10–6 m
(c) 10–15 m
(d) 10–14 m

Answer Answer: (d) Nuclear radius = 1014 m.

Q.4. Particles which can be added to the nucleus of an atom
without changing its chemical properties are called
(a) neutrons
(b) electrons
(c) protons
(d) alpha particles

Answer Answer: (a) Chemical properties are unaffected with addition of neutrons to the nucleus.

Q.5. The radius of a nucleus is
(a) directly proportional to its mass number
(b) inversely proportional to its atomic weight
(c) directly proportional to the cube root of its mass number
(d) None of these

Answer Answer: (c) R = R0A1/3

Q.6. Nucleus of an atom whose atomic mass is 24 consists of
(a) 11 electrons, 11 protons and 13 neutrons
(b) 11 electrons, 13 protons and 11 neutrons
(c) 11 protons and 13 neutrons
(d) 11 protons and 13 electrons

Answer Answer: (c) Nucleus does not contain electron.

Q.7. The electrons cannot exist inside the nucleus because
(a) de-Broglie wavelength associated with electron in β -decay is much less than the size of nucleus
(b) de-Broglie wavelength associated with electron in β -decay is much greater than the size of nucleus
(c) de-Broglie wavelength associated with electron in β -decay is equal to the size of nucleus
(d) negative charge cannot exist in the nucleus

Answer Answer: (b)

Q.8. In …X… water is circulated though the reactor vessel and transfers energy to steam generator in the …Y… Here, X and Y refer to
(a) primary loop, secondary loop
(b) reactor core, turbine
(c) secondary loop, primary loop
(d) turbine, reactor core

Answer Answer: (a) In pressurised-water, nuclear reactor, in primary loop water is circulated through the reactor vessel and transfers energy to steam generator in secondary loop.

Q.9. A nuclei having same number of neutron but different
number of protons / atomic number are called
(a) isobars
(b) isomers
(c) isotones
(d) isotopes

Answer Answer: (c)

Q.10. Which one of the following has the identical property for isotopes?
(a) Physical property
(b) Chemical property
(c) Nuclear property
(d) Thermal property

Answer Answer: (b)

Q.11. The number of protons in an atom of atomic number Z
and mass number A is
(a) zero
(b) Z
(c) A – Z
(d) A

Answer Answer: (b)

Q.12. When the number of nucleons in nuclei increases, the
binding energy per nucleon
(a) increases continuously with mass number
(b) decreases continuously with mass number
(c) remains constant with mass number
(d) first increases and then decreases with increase of mass number

Answer Answer: (d) Average BE/nucleon increases first, and then decreases, as is clear from BE curve.

Q.13. Mp denotes the mass of a proton and Mn that of a neutron.
A given nucleus, of binding energy B, contains Z protons
and N neutrons. The mass M(N, Z) of the nucleus is given
by (c is the velocity of light)
(a) M(N, Z) = NMn + ZMp + B/c2
(b) M(N, Z) = NMn + ZMp – Bc2
(c) M(N, Z) = NMn + ZMp + Bc2
(d) M(N, Z) = NMn + ZMp – B/c2

Answer Answer: (d) Mass defect = B.E./c2

Mass of nucleus = Mass of proton + mass of neutron – mass defect

Q.14. Mass energy equation was propounded by
(a) Newton
(b) Madam Curie
(c) C. V. Raman
(d) Einstein

Answer Answer: (d)

Q.15. The mass of an atomic nucleus is less than the sum of the masses of its constituents. This mass defect is converted into
(a) heat energy
(b) light energy
(c) electrical energy
(d) energy which binds nucleons together

Answer Answer: (d)

Q.16. Which of the following statement is not true regarding
Einsteins mass energy relation?
(a) Mass disappears to reappear as energy.
(b) Energy disappears to reappear as mass.
(c) Mass and energy are two different forms of the same entity.
(d) Mass and energy can never be related to each other.

Answer Answer: (d)

Q.17. The curve of binding energy per nucleon as a function of atomic mass number has a sharp peak for helium nucleus. This implies that helium
(a) can easily be broken up
(b) is very stable
(c) can be used as fissionable material
(d) is radioactive

Answer Answer: (b)

Q.18. Nuclear forces are
(a) spin dependent and have no non-central part
(b) spin dependent and have a non-central part
(c) spin independent and have no non-central part
(d) spin independent and have a non-central part

Answer Answer: (b)

Q.19. Nuclear forces exists between
(a) neutron – neutron
(b) proton – proton
(c) neutron – proton
(d) all of these

Answer Answer: (d)

Q.20. The antiparticle of electron is
(a) positron
(b) α-particle
(c) proton
(d) β-particle

Answer Answer: (a) Antiparticle of electron (–1e0) is positron (+1e0)

Q.21. Neutron decay in free space is given as follows
0n11H1 + -1e0 + []
Then the parenthesis [ ] represents a
(a) neutrino
(b) photon
(c) antineutrino
(d) graviton

Answer Answer: (c) An electron is accompanied by an antineutrino.

Q.22. Radioactivity is
(a) irreversible process
(b) self disintegration process
(c) spontaneous
(d) all of the above

Answer Answer: (d) All the characteristics given are true for radioactivity.

Q.23. γ-rays are deflected by
(a) an electric field but not by a magnetic field
(b) a magnetic field but not by an electric field
(c) both electric and magnetic field
(d) neither by electric field nor by magnetic field

Answer Answer: (d) γ-rays carry no charge. They are neither deflected by an electric field nor by a magnetic field.

Q.24. Beta rays emitted by a radioactive material are
(a) electromagnetic radiations
(b) the electrons orbiting around the nucleus
(c) charged particles emitted by nucleus
(d) neutral particles

Answer Answer: (c) β-rays are charged particles emitted by nucleus.

Q.25. Which of the following is not a mode of radioactive decay ?
(a) Positron emission
(b) Electron capture
(c) Fusion
(d) Alpha decay

Answer Answer: (c) Fusion is not a mode of decay.

Q.26. The half-life period and the mean life period of a radioactive
element are denoted respectively by Th and Tm. Then
(a) Th = Tm
(b) Th > Tm
(c) Th < Tm
(d) Th ≥ Tm

Answer Answer: (c)

Q.27. In γ ray emission from a nucleus
(a) only the proton number changes
(b) both the neutron number and the proton number
change
(c) there is no change in the proton number and the
neutron number
(d) only the neutron number changes

Answer Answer: (c)

Q.28. Artificial radioactivity was discovered by
(a) Klaproth
(b) Rontgen
(c) Irene Curie and Joliot
(d) P. Curie and M. Curie

Answer Answer: (c)

Q.29. Radioactive samples are stored in lead boxes because it is
(a) heavy
(b) strong
(c) good absorber
(d) bad conductor

Answer Answer: (c)

Q.30. The process of radioactive radiations remains unaffected due to
(a) physical changes
(b) chemical changes
(c) electric or magnetic fields
(d) all of the above

Answer Answer: (d)

Q.31. A radioactive material undergoes decay by ejecting electrons. The electron ejected in this process is
(a) the electron from the decay of a neutron
(b) the electron present in the nucleus
(c) the resulting from the conversion of 􀁊 photon
(d) an orbital electron

Answer Answer: (a)

Q.32. The same radioactive nucleus may emit
(a) all the three α, β and γ one after another
(b) all the three α, β and γ radiations simultaneously
(c) only α and βsimultaneously
(d) only one α, β and γ at a time

Answer Answer: (d)

Q.33. Which of the following of a radioactive material is a
measure of its instability?
(a) Full life
(b) Mean life
(c) Half life
(d) None of these

Answer Answer: (c)

Q.34. The rate of disintegration at a given instant, is directly proportional to the number of atoms present at that instant. This is the statement of
(a) law of radioactive decay
(b) half life
(c) law of radioactive transformation
(d) group displacement law

Answer Answer: (a)

Q.35. Three specimens A, B, C of same radioactive element has activities 1 microcurie, 1 rutherford and 1 becquerel respectively. Which specimen has maximum mass?
(a) A
(b) B
(c) C
(d) all have equal masses

Answer Answer: (b) Activity is proportional to mass. Activity of specimen B is maximum. Thus, mass of specimen B is also maximum.

Q.36. If a radioactive element is placed in an evacuated
chamber, then the rate of radioactive decay will
(a) decrease (b) remains unchanged
(c) increase (d) none of these

Answer Answer: (b) Activity is proportional to mass. Activity of specimen B is maximum. Thus, mass of specimen B is also maximum.

Q.37. The 􀁊 radiations are
(a) electromagnetic radiation with high energy
(b) electromagnetic radiation with low energy
(c) charged particles emitted by the nucleus
(d) electrons orbiting the nucleus

Answer Answer: (a)

Q.38. Radioactive substance emits
(a) α-rays
(b) β-rays
(c) γ-rays
(d) All of the above

Answer Answer: (d)

Q.39. The ‘rad’ is the correct unit used to report the measurement
of
(a) the ability of a beam of gamma ray photons to produce
ions in a target
(b) the energy delivered by radiation to a target
(c) the biological effect of radiation
(d) the rate of decay of a radioactive source

Answer Answer: (c) The risk posed to a human being by any radiation exposure depends partly upon the absorbed dose, the amount of energy absorbed per gram of tissue. Absorbed dose is expressed in rad. A rad is equal to 100 ergs of energy absorbed by 1 gram of tissue. The more modern, internationally adopted unit is the gray (named after the English medical physicist L. H. Gray); one gray equals 100 rad.

Q.40. One curie is equal to
(a) 3.7 × 1010 disintegration/sec
(b) 3.2 × 108 disintegration/sec
(c) 2.8 × 1010 disintegration/sec
(d) None of these

Answer Answer: (a)

Q.41. Half life of radioactive element depends upon
(a) amount of element present
(b) temperature
(c) pressure
(d) nature of element

Answer Answer: (d) Half life of a substance doesn’t depends upon amount, temperature and pressure. It depends upon the nature of the substance.

Q.42. A nuclear reaction is given by
ZXAZ+1YA + -1e0 + ν̅
(a) fission
(b) β-decay
(c) σ -decay
(d) fusion

Answer Answer: (b)

Q.43. Fusion reaction occurs at temperatures of the order of
(a) 103 K (b) 107 K (c) 10 K (d) 104 K

Answer Answer: (b)

Q.44. Control rods used in nuclear reactors are made of
(a) stainless steel (b) graphite
(c) cadmium (d) plutonium

Answer Answer: (c) Control rods are made of cadmium.

Q.45. Boron rods in a nuclear reactor are used to
(a) absorb excess neutrons
(b) absorb alpha particle
(c) slow down the reaction
(d) speed up the reaction

Answer Answer: (a) Boron rods absorb excess neutrons.

Q.46. A moderator is used in nuclear reactors in order to
(a) slow down the speed of the nuetrons
(b) acceleerate the neutrons
(c) increase the number of neutrons
(d) decrease the number of neutrons

Answer Answer: (c) Moderator slows down neutrons.

Q.47. Fusion reactions take place at high temperature because
(a) atoms are ionised at high temperature
(b) molecules break up at high temperature
(c) nuclei break up at high temperature
(d) kinetic enrgy is high enough to overcome repulsion
between nuclei

Answer Answer: (d) Extremely high temps needed for fusion make K.E. large enough to overcome repulsion between nuclei.

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