CBSE Class 12 Physics Nuclei MCQs Set A

Question : The constituents of nucleus are

(a) electrons and protons
(b) protons and neutrons
(c) neutrons and electrons
(d) electrons, protons and neutrons

Answer: B 

Question : 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: C 

Question : 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: C 

Question : 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: D 

Question : 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: D 

Question : 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: D 

Question : On an average, the number of neutrons and the energy of a neutron released per fission of a uranium atom are respectively

(a) 2.5 and 2 keV
(b) 3 and l keV
(c) 2.5 and 2 MeV
(d) 2 and 2 keV

Answer: C 

Question : 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: C 

Question : 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: D

Question : 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: C 

Question : Chadwick was awarded the 1935 nobel prize in physics for his discovery of the
(a) electron
(b) proton
(c) neutron
(d) positron
Answer: C

Question : If a star can convert all the He nuclei completely into oxygen nuclei. The energy released per oxygen nuclei is [Mass of He nucleus is 4.0026 amu and mass of Oxygen nucleus is 15.9994 amu]
(a) 7.6 MeV   
(b) 56.12 MeV
(c) 10.24 MeV
(d) 23.9 MeV

Answer: C 

Question : If 200 MeV energy is released in the fission of a single U235 nucleus, the number of fissions required per second to produce 1 kilowatt power shall be (Given 1eV = 1.6 × 10^–19 J)
(a) 3.125 × 10¹³
(b) 3.125 × 10¹⁴
(c) 3.125 × 10¹⁵
(d) 3.125 × 10¹⁶

Answer: A

Question : A certain mass of Hydrogen is changed to Helium by the process of fusion. The mass defect in fusion reaction is 0.02866 a.m.u. The energy liberated per a.m.u. is (Given : 1 a.m.u = 931 MeV)
(a) 26.7 MeV
(b) 6.675 MeV
(c) 13.35 MeV
(d) 2.67 MeV

Answer: B 

Question : Radioactivity is
(a) irreversible process
(b) self disintegration process
(c) spontaneous
(d) all of the above

Answer: D 

Question : 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: C

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

Answer: C

Question : 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 g photon
(d) an orbital electron

Answer: A

Question : 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: A

Question : Half life of radioactive element depends upon
(a) amount of element present
(b) temperature
(c) pressure
(d) nature of element

Answer: D

Question : A freshly prepared radioactive source of half life 2 hr emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is
(a) 6 hr
(b) 12 hr
(c) 24 hr
(d) 128 hr

Answer: B