CBSE Class 12 Physics Atoms And Nuclie Boards Questions Worksheet

Important Questions for NCERT Class 12 Physics Nuclei  

Question. Mn and Mp represent the mass of neutron and proton respectively. An element having mass M has N neutrons and Z protons, then the correct relation will be
(a) M < {N · Mn + Z · Mp}
(b) M > {N · Mn + Z · Mp}
(c) M = {N · Mn + Z · Mp}
(d) M = N {Mn + Mp} 

Answer  :  A

Question. Energy released in nuclear fission is due to
(a) some mass is converted into energy
(b) total binding energy of fragments is more than the binding energy of parental element
(c) total binding energy of fragments is less than the binding energy of parental element
(d) total binding energy of fragments is equal to the binding energy of parental element. 

Answer  :  A

Question. The binding energy per nucleon is maximum in case of
(a) ⁴₂He
(b) ⁵⁶₂₆Fe
(c) ¹⁴¹₅₆Ba
(d) ²³⁵₉₂U

Answer  :  B

Question. The energy equivalent of one atomic mass unit is
(a) 1.6 × 10–19 J
(b) 6.02 × 1023 J
(c) 931 MeV
(d) 9.31 MeV 

Answer  :  C

Question. The average binding energy of a nucleon inside an atomic nucleus is about
(a) 8 MeV
(b) 8 eV
(c) 8 J
(d) 8 erg

Answer  :  A

Question. If the nuclear force between two protons, two neutrons and between proton and neutron is denoted by Fpp, Fnn and Fpn respectively, then
(a) Fpp Fnn Fpn
(b) Fpp ≠ Fnn and Fpp = Fnn
(c) Fpp = Fnn = Fpn
(d) Fpp ≠ Fnn ≠ Fpn 

Answer  :  C

Question. Which of the following statements is true for nuclear forces?
(a) They obey the inverse square law of distance.
(b) They obey the inverse third power law of distance.
(c) They are short range forces.
(d) They are equal in strength to electromagnetic forces.

Answer  :  C

Question. a-particle consists of
(a) 2 protons only
(b) 2 protons and 2 neutrons only
(c) 2 electrons, 2 protons and 2 neutrons
(d) 2 electrons and 4 protons only 

Answer  :  B

Question. The rate of radioactive disintegration at an instant for a radioactive sample of half life 2.2 × 10⁹ s is 10¹⁰ s^–1. The number of radioactive atoms in the sample at that instant is,

(a) 3.17 × 1020
(b) 3.17 × 1017
(c) 3.17 × 1018
(d) 3.17 × 1019

Answer  :  D

Question. For a radioactive material, half-life is 10 minutes.If initially there are 600 number of nuclei, the time taken (in minutes) for the disintegration of 450 nuclei is
(a) 20
(b) 10
(c) 30
(d) 15

Answer  :  A

Question. The half-life of a radioactive substance is 30 minutes.
The time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is
(a) 15
(b) 30
(c) 45
(d) 60

Answer  :  D

Question. A nucleus of uranium decays at rest into nuclei of thorium and helium. Then
(a) The helium nucleus has more momentum than the thorium nucleus.
(b) The helium nucleus has less kinetic energy than the thorium nucleus.
(c) The helium nucleus has more kinetic energy than the thorium nucleus.
(d) The helium nucleus has less momentum than the thorium nucleus.

Answer  :  C

Question. A radioisotope X with a half life 1.4 × 109 years decays to Y which is stable. A sample of the rock from a cave was found to contain X and Y in the ratio 1 : 7. The age of the rock is
(a) 1.96 × 109 years
(b) 3.92 × 109 years
(c) 4.20 × 109 years
(d) 8.40 × 109 years

Answer  :  C

Question. The half life of a radioactive isotope ‘X’ is 20 years.
It decays to another element ‘Y’ which is stable. The two elements ‘X’ and ‘Y’ were found to be in the ratio 1 : 7 in a sample of a given rock. The age of the rock is estimated to be
(a) 80 years
(b) 100 years
(c) 40 years
(d) 60 years

Answer  :  D

Question. a-particles, b-particles and g-rays are all having same energy. Their penetrating power in a given medium in increasing order will be
(a) g, a, b
(b) a, b, g
(c) b, a, g
(d) b, g, a

Answer  :  B

Question. A mixture consists of two radioactive materials A1 and A2 with half lives of 20 s and 10 s respectively.
Initially the mixture has 40 g of A1 and 160 g of A2.
The amount of the two in the mixture will become equal after
(a) 60 s
(b) 80 s
(c) 20 s
(d) 40 s 

Answer  :  D

Question. The half life of a radioactive nucleus is 50 days. The time interval (t2 – t1) between the time t2 when 2/3 of it has decayed and the time t1 when 1/3 of it had decayed is
(a) 30 days
(b) 50 days
(c) 60 days
(d) 15 days 

Answer  :  B

Question. The half life of a radioactive isotope X is 50 years. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio of 1 : 15 in a sample of a given rock. The age of the rock was estimated to be
(a) 150 years
(b) 200 years
(c) 250 years
(d) 100 years

Answer  :  B

Question. A radioactive nucleus of mass M emits a photon of frequency u and the nucleus recoils. The recoil energy will be
(a) Mc² – hu
(b) h²ν²/2Mc²
(c) zero
(d) hν

Answer  :  B

Question. 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  :  C

Question. Two radioactive materials X1 and X2 have decay constants 5l and l respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X1 to that X2 will be 1/e after a time

(a) 1/4λ
(b) e/λ
(c) λ
(d) 1/2λ

Answer  :  A

Question. Two radioactive substances A and B have decay constants 5l and l respectively. At t = 0 they have the same number of nuclei. The ratio of number of nuclei of A to those of B will be (1/e)2 after a time interval
(a) 4λ
(b) 2λ
(c) 1/2λ
(d) 1/4λ

Answer  :  C

Question. In a radioactive decay process, the negatively charged emitted b-particles are
(a) the electrons produced as a result of the decay of neutrons inside the nucleus
(b) the electrons produced as a result of collisions between atoms
(c) the electrons orbiting around the nucleus
(d) the electrons present inside the nucleus.

Answer  :  A

Question. In a radioactive material the activity at time t1 is R1 and at a later time t2, it is R2. If the decay constant of the material is l, then
(a) R1 = R₂
(b) R₁ R₂e ^{-λ(t₁- t₂)}
(c) R₁ = R₂e  ^{-λ(t₁- t₂)}
(d) R₁ = R₂(t₂/t₁) 

Answer  :  B