CBSE Class 12 Physics Atoms And Nuclie Important Questions Worksheet

Q1. Define Nuclear forces and gives their important characteristics/properties.

Ans.The nucleus of an atom has a number of protons and neutrons (nucleons) which are held together by the forces known as Nuclear forces in the tiny nucleus, inspite of strong force of repulsion between protons. Characteristics/Properties of nuclear forces:

1. Nuclear forces are strongest forces in nature.

2. Nuclear forces are short range forces.

3. Nuclear forces are basically strong attractive forces but contain a small component of repulsive forces.

4. Nuclear forces are saturated forces.

5. Nuclear forces are charge independent

6. Nuclear forces are spin- dependent

7. Nuclear forces are exchange forces

 Important Questions for NCERT Class 12 Physics Atoms

Question. The energy of the ground electronic state of hydrogen atom is –13.6 eV. The energy of the first excited state will be

(a) –27.2 eV
(b) –52.4 eV
(c) –3.4 eV
(d) –6.8 eV

Answer :   C

Question. When hydrogen atom is in its first excited level, its radius is .......... of the Bohr radius.
(a) twice
(b) 4 times
(c) same
(d) half 

Answer :   B

Question. According to Bohr’s principle, the relation between principal quantum number (n) and radius of orbit (r) is
(a) r ∝ 1/n
(b) r ∝ 1/n²
(c) r ∝ n
(d) r ∝ n2 

Answer :   D

Question. When a hydrogen atom is raised from the ground state to an excited state,
(a) both K.E. and P.E. increase
(b) both K.E. and P.E. decrease
(c) the P.E. decreases and K.E. increases
(d) the P.E. increases and K.E. decreases. 

Answer :   D

Question. In terms of Bohr radius a0, the radius of the second Bohr orbit of a hydrogen atom is given by
(a) 4a0
(b) 8a0
(c) 2a0
(d) 2a0 

Answer :   A

Question. The ionization energy of hydrogen atom is 13.6 eV.
Following Bohr’s theory, the energy corresponding to a transition between 3rd and 4th orbit is
(a) 3.40 eV
(b) 1.51 eV
(c) 0.85 eV
(d) 0.66 eV 

Answer :   D

Question. The ground state energy of H-atom is –13.6 eV. The energy needed to ionize H-atom from its second excited state
(a) 1.51 eV
(b) 3.4 eV
(c) 13.6 eV
(d) none of these 

Answer :   A

Question. Which one did Rutherford consider to be supported by the results of experiments in which a-particles were scattered by gold foil? 
(a) The nucleus of an atom is held together by forces which are much stronger than electrical or gravitational forces.
(b) The force of repulsion between an atomic nucleus and an a-particle varies with distance according to inverse square law.
(c) a-particles are nuclei of Helium atoms.
(d) Atoms can exist with a series of discrete energy levels

Answer :   B

Question. As an electron makes a transition from an excited state to the ground state of a hydrogen - like atom/ion 
(a) kinetic energy decreases, potential energy increases but total energy remains same
(b) kinetic energy and total energy decrease but potential energy increases
(c) its kinetic energy increases but potential energy and total energy decrease
(d) kinetic energy, potential energy and total energy decrease

Answer :   C

Question. To explain his theory, Bohr used
(a) conservation of linear momentum
(b) quantisation of angular momentum
(c) conservation of quantum frequency
(d) none of these

Answer :   B

Question. The ionisation energy of hydrogen atom is 13.6 eV,the ionisation energy of a singly ionised helium atom would be
(a) 13.6 eV
(b) 27.2 eV
(c) 6.8 eV
(d) 54.4 eV

Answer :   D

Question. If an electron in a hydrogen atom jumps from the 3rd orbit to the 2nd orbit, it emits a photon of wavelength l. When it jumps from the 4th orbit to the 3rd orbit, the corresponding wavelength of the photon will be
(a) 16/25λ
(b) 9/16λ
(c) 20/7λ
(d) 20/13λ

Answer :   C

Important Questions for NCERT Class 12 Physics Nuclei 

Question. In the nucleus of ₁₁Na²³, the number of protons, neutrons and electrons are
(a) 11, 12, 0
(b) 23, 12, 11
(c) 12, 11, 0
(d) 23, 11, 12 

Answer  :  A

Question. The nuclei ₆C¹³ and ₇N¹⁴ can be described as
(a) isotones
(b) isobars
(c) isotopes of carbon
(d) isotopes of nitrogen

Answer  :  A

Question. If the nuclear radius of 27Al is 3.6 fermi, the approximate nuclear radius of 64Cu in fermi is
(a) 2.4
(b) 1.2
(c) 4.8
(d) 3.6

Answer  :  C

Question. Two nuclei have their mass numbers in the ratio of 1 : 3. The ratio of their nuclear densities would be
(a) (3)1/3 : 1
(b) 1 : 1
(c) 1 : 3
(d) 3 : 1 

Answer  :  B

Question. If the nucleus ²⁷₁₃Al has a nuclear radius of about 3.6 fm, then 32 125Te would have its radius approximately as
(a) 9.6 fm
(b) 12.0 fm
(c) 4.8 fm
(d) 6.0 fm 

Answer  :  D

Question. The radius of germanium (Ge) nuclide is measured to be twice the radius of ⁹₄Be. The number of nucleons in Ge are
(a) 72
(b) 73
(c) 74
(d) 75 

Answer  :  A

Question. The volume occupied by an atom is greater than the volume of the nucleus by a factor of about
(a) 101
(b) 105
(c) 1010
(d) 1015 

Answer  :  D

Question. A nucleus ruptures into two nuclear parts, which have their velocity ratio equal to 2 : 1. What will be the ratio of their nuclear size (nuclear radius)?
(a) 31/2 : 1
(b) 1 : 31/2
(c) 21/3 : 1
(d) 1 : 21/3 

Answer  :  D

Question. The mass number of He is 4 and that of sulphur is 32. The radius of sulphur nucleus is larger than that of helium by the factor of
(a) 4
(b) 2
(c) 8
(d) 8 

Answer  :  B

Question. The mass density of a nucleus varies with mass number A as
(a) A2
(b) A
(c) constant
(d) 1/A 

Answer  :  C

Question. The ratio of the radii of the nuclei 13Al27 and 52Te125 is approximately
(a) 6 : 10
(b) 13 : 52
(c) 40 : 177
(d) 14 : 73

Answer  :  A

Question. The energy required to break one bond in DNA is 10–20 J. This value in eV is nearly
(a) 6
(b) 0.6
(c) 0.06
(d) 0.006

Answer  :  C

Question. The energy equivalent of 0.5 g of a substance is
(a) 4.5 × 1016 J
(b) 4.5 × 1013 J
(c) 1.5 × 1013 J
(d) 0.5 × 1013 J

Answer  :  B

Question. How does the Binding Energy per nucleon vary with the increase in the number of nucleons?
(a) Decrease continuously with mass number.
(b) First decreases and then increases with increase in mass number.
(c) First increases and then decreases with increase in mass number.
(d) Increases continuously with mass number.

Answer  :  C

Question. The mass of a ⁷₃Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of 37Li nucleus is nearly
(a) 46 MeV
(b) 5.6 MeV
(c) 3.9 MeV
(d) 23 MeV 

Answer  :  B

Question. If M(A; Z), Mp and Mn denote the masses of the nucleus Z
A X, proton and neutron respectively in units of u (1 u = 931.5 MeV/c²) and BE represents its binding energy in MeV, then
(a) M(A, Z) = ZMp + (A – Z)Mn – BE
(b) M(A, Z) = ZMp + (A – Z)Mn + BE/c²
(c) M(A, Z) = ZMp + (A – Z)Mn – BE/c²
(d) M(A, Z) = ZMp + (A – Z)Mn + BE

Answer  :  C

Question. A nucleus Z
AX has mass represented by M(A, Z).
If Mp and Mn denote the mass of proton and neutron respectively and B.E. the binding energy in MeV, then
(a) B.E. = [ZMp + (A – Z)Mn – M(A, Z)]c2
(b) B.E. = [ZMp + AMn – M(A, Z)]c2
(c) B.E. = M(A, Z) – ZMp – (A – Z)Mn
(d) B.E. = [M(A, Z) – ZMp – (A – Z)Mn]c2 

Answer  :  A

Question. Fission of nuclei is possible because the binding energy per nucleon in them
(a) increases with mass number at low mass numbers
(b) decreases with mass number at low mass numbers
(c) increases with mass number at high mass numbers
(d) decreases with mass number at high mass numbers. 

Answer  :  D

Question. The mass of proton is 1.0073 u and that of neutron is 1.0087 u (u = atomic mass unit). The binding energy of 24He is (Given helium nucleus mass ≈ 4.0015 u)
(a) 0.0305 J
(b) 0.0305 erg
(c) 28.4 MeV
(d) 0.061 u

Answer  :  C

Question. Which of the following are suitable for the fusion process?
(a) Light nuclei
(b) Heavy nuclei
(c) Element lying in the middle of the periodic table
(d) Middle elements, which are lying on binding energy curve.

Answer  :  A

Please click the link below to download CBSE Class 12 Physics Atoms and Nuclie Important Questions .