CBSE Class 12 Physics Nuclei Worksheet Set B

Important Questions for NCERT Class 12 Physics Nuclei 

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. Which rays contain (positive) charged particles?
(a) a-rays
(b) b-rays
(c) g-rays
(d) X-rays

Answer: A

Question. Half life of a radioactive element is 12.5 hours and its quantity is 256 g. After how much time its quantity will remain1 g?
(a) 50 hrs
(b) 100 hrs
(c) 150 hrs
(d) 200 hrs

Answer: B

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 ₃⁷Li 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 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. Which of the following statements is true?
(a) ₇₈Pt¹⁹² has 78 neutrons
(b) ₈₄Po²¹⁴ → ₈₂Pb²¹⁰ + β–
(c) ₉₂U²³⁸ → ₉₀Th²³⁴ + ₂He⁴
(d) ₉₀Th²³⁴ → ₉₁Pa²³⁴ + ₂He4

Answer: C

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

Question. Radioactive material 'A' has decay constant '8 λ' and material 'B' has decay constant 'λ'. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material 'B' to that 'A' will be 1/e
(a) 1/7λ
(b) 1/8λ
(c) 1/9λ
(d) 1/λ

Answer: A

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

Answer: B

Question. The intensity of gamma radiation from a given source is I₀. On passing through 37.5 mm of lead it is reduced to I₀/8.
The thickness of lead which will reduce it to I₀/2 is
(a) (37.5)^1/3 mm
(b) (37.5)^1/4 mm
(c) 37.5/3 mm
(d) (37.5/4) mm

Answer: C

Question. Which of the following has the mass closest in value to that of the positron? (1 a.m.u. = 931 MeV)
(a) Proton
(b) Electron
(c) Photon
(d) Neutrino

Answer: B

Question. Radioactive element decays to form a stable nuclide, then the rate of decay of reactant is 

Answer: C

Question. A radioactive nucleus undergoes α -emission to form a stable element. What will be the recoil velocity of the daughter nucleus if v is the velocity of α emission?
(a) 4v/A - 4 
(b) 2v/A - 4 
(c) 4v/A + 4
(d) 2v/A + 4

Answer: A

Question. 1 g of hydrogen is converted into 0.993 g of helium in a thermonuclear reaction. The energy released is
(a) 63 × 10⁷ J
(b) 63 × 10¹⁰ J
(c) 63 × 10¹⁴ J
(d) 63 × 10²⁰ J

Answer: B

Question. Radium ²²⁶Ra, spontaneously decays to radon with the emission of an α-particle and a γ ray. If the speed of the a particle upon emission from an initially stationary radium nucleus is 1.5 ×10⁷ m/s, what is the recoil speed of the resultant radon nucleus? Assume the momentum of γ ray is negligible compared to that of α particle.
(a) 2..0 × 10⁵ m/s
(b) 2.7 × 10⁵ m/s
(c) 3.5 × 10⁵ m/s
(d) 1.5 × 10⁷ m/s

Answer: B

Question. The energy released per fission of a ₉₂U²³⁵ nucleus is nearly 
(a) 200 eV
(b) 20 eV
(c) 200 MeV
(d) 2000 eV

Answer: C

Question. At time t = 0, N₁ nuclei of decay constant λ1 and N₂ nuclei of decay constant λ₂ are mixed. The decay rate of mixture is 

Answer: D

Question. If the radius of a nucleus ²⁵⁶X is 8 fermi, then the radius of ⁴He nucleus will be
(a) 16 fermi
(b) 2 fermi
(c) 32 fermi
(d) 4 fermi

Answer: B

Question. Order of magnitude of density of uranium nucleus is (m_p = 1.67 × 10^–27 kg)
(a) 10²⁰ kg / m³
(b) 10¹⁷ kg / m³
(c) 10¹⁴ kg / m³
(d) 10¹¹ kg / m³

Answer: B

Question. Outside a nucleus
(a) neutron is stable
(b) proton and neutron both are stable
(c) neutron is unstable
(d) neither neutron nor proton is stable

Answer: C

Question. The binding energy per nucleon for 2₁ H and 4₂ He respectively are 1.1 MeV and 7.1 MeV. The energy released in MeV when two 2₁ H nuclei fuse to form 4₂ He is
(a) 4.4
(b) 8.2
(c) 24
(d) 28.4

Answer: C

Question. The rest energy of an electron is
(a) 510 KeV
(b) 931 KeV
(c) 510 MeV
(d) 931 MeV

Answer: A

Question. 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: A

Question. In which sequence the radioactive radiations are emitted in the following nuclear reaction? 

(a) γ, α, β
(b) α, β, γ
(c) β, γ, α
(d) β, α, γ

Answer: D

Question. A radioactive element forms its own isotope after 3 consecutive disintegrations. The particles emitted are
(a) 3 β–particles
(b) 2 β–particles and 1 α–particle
(c) 3 β–particles and 1 α–particle
(d) 2 α–particles and 1 β–particle.

Answer: B

Question. If u denotes 1 atomic mass unit. One atom of an element has mass exactly equal to Au, where A is mass number of element.
(a) A = 1
(b) A = 12
(c) A = 16
(d) A can take up any integral value from 1 to 110

Answer: B

Question. From the following equations, pick out hte possible nuclear reactions.
(a) ₆C¹³ + ₁H¹ → ₆C¹⁴ + 4.3 MeV
(b) ₆C¹² + ₁H¹ → ₇N¹³ + 2 MeV
(c) ₇N¹⁴ + ₁H¹ → ₈O¹⁵ + 7.3 MeV
(d) ₉₂U²³⁵ + ₀n¹ → ₅₄X¹⁴⁰ + ₃₈Si⁹⁴ + ₂₀n¹ + γ + 200 MeV

Answer: B,C

Question. In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. the moderator used have light nuclei. Heavy nuclei will not serve the purpose, because
(a) they will break up
(b) elastic collision of neutrons with heavy nuclei will not slow them down
(c) the net weight of the reactor would be unbearably high
(d) substances with heavy nuclei do not occur in liquid or gaseous state at room temperature

Answer: B

Question. 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) = NM_n + ZM_p + B/c²
(b) M(N, Z) = NM_n + ZM_p – Bc²
(c) M(N, Z) = NM_n + ZM_p + Bc²
(d) M(N, Z) = NM_n + ZM_p – B/c²

Answer: D

Question. Atomic weight of boron is 10.81 and it has two isotopes ₅B¹⁰ and ₅B¹¹. Then ratio of ₅B¹⁰ : ₅B¹¹ in nature would be
(a) 19 : 81
(b) 10 : 11
(c) 15 : 16
(d) 81 : 19

Answer: A

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. X(n, a) 37Li, then X will be
(a) ₅¹⁰B
(b) ₅⁹B
(c) ₄¹¹Be
(d) ₂⁴He

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 2 4He 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

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

Answer: B

Question. Two radioactive nuclei P and Q, in a given sample decay into a stable nucleus R. At time t = 0, number of P species are 4 N0 and that of Q are N0 . Half-life of P (for conversion to R) is 1 minute where as that of Q is 2 minutes. Initially there are no nuclei of R present in the sample. When number of nuclei of P and Q are equal, the number of nuclei of R present in the sample would be
(a) 2 N₀
(b) 3 N₀
(c) 9 N₀ /2
(d) 5 N₀ /2

Answer: C

Question. The half life of radium is about 1600 years. If 100 g of radium existing now, 25 g will remain unchanged after
(a) 4800 years
(b) 6400 years
(c) 2400 years
(d) 3200 years 

Answer: D

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. A sample of radioactive element has a mass of 10 g at an instant t = 0. The approximate mass of this element in the sample after two mean lives is
(a) 1.35 g
(b) 2.50 g
(c) 3.70 g
(d) 6.30 g

Answer: A

Question. The power obtained in a reactor using U²³⁵disintegration is 1000 kW. The mass decay of U²³⁵ per hour is
(a) 10 microgram
(b) 20 microgram
(c) 40 microgram
(d) 1 microgram 

Answer: C

Question. If in a nuclear fusion process the masses of the fusing nuclei be m1 and m2 and the mass of the resultant nucleus be m3, then
(a) m3 = m1 + m₂
(b) m3 = |m1 – m₂|
(c) m3 < (m1 + m₂)
(d) m3 > (m1 + m2)

Answer: C

Question. Solar energy is mainly caused due to
(a) burning of hydrogen in the oxygen
(b) fission of uranium present in the Sun
(c) fusion of protons during synthesis of heavier elements
(d) gravitational contraction 

Answer: C

Question. Nuclear fission is best explained by
(a) liquid droplet theory
(b) Yukawa p-meson theory
(c) independent particle model of the nucleus
(d) proton-proton cycle. 

Answer: A

Question. Which of the following is used as a moderator in nuclear reaction?
(a) Cadmium
(b) Plutonium
(c) Uranium
(d) Heavy water 

Answer: D

Question. Energy released in the fission of a single ₉₂²³⁵U nucleus is 200 MeV. The fission rate of ₉₂²³⁵U filled reactor operating at a power level of 5 W is
(a) 1.56 × 10^–10 s^–1
(b) 1.56 × 10¹¹ s^–1
(c) 1.56 × 10^–16 s^–1
(d) 1.56 × 10^–17 s–1

Answer: B

Question. Solar energy is due to
(a) fusion reaction
(b) fission reaction
(c) combustion reaction
(d) chemical reaction

Answer: A

Question. Fusion reaction takes place at high temperature because
(a) nuclei break up at high temperature
(b) atoms get ionised at high temperature
(c) kinetic energy is high enough to overcome the coulomb repulsion between nuclei
(d) molecules break up at high temperature

Answer: C

Question. The binding energy per nucleon in deuterium and helium nuclei are 1.1 MeV and 7.0 MeV, respectively.
When two deuterium nuclei fuse to form a helium nucleus the energy released in the fusion is
(a) 23.6 MeV
(b) 2.2 MeV
(c) 28.0 MeV
(d) 30.2 MeV

Answer: A
 

1 Define total decay rate of a radioactive substance. Also give an expression for finding the same .Plot a graph showing the variation of number of undecayed nuclei with time 

2 Define SI unit of measurement of activity of a radioactive substance. What is the relationship between curie and Becquerel

3 What is meant by Half-life period of a radioactive substance? Give an expression for finding the same. What is the difference between Half-life and mean life of a radioactive substance?

4 The half-life of 92U232 undergoing α-decay is 4.5 X 109years. What is the activity of 1g sample of 92U232?

5 Tritium has a half-life of 12.5 years undergoing beta decay. What fraction of a sample of pure tritium will remain undecayed after 25 years?

6 What is meant by disintegration energy of a nuclear reaction? Find the value of the same for an α- decay?

7 Give an example of a reaction showing β+ decay and β- decay.

8 Give any three properties of neutrinos.

9 What is the difference between β+ decay and β- decay?

10 Discuss the stability of a free neutron

11 What is the difference in the order of the atomic and nuclear energy levels

12 Explain briefly how gamma decay takes place by giving an example.

13 What is the difference between a chemical reaction and a nuclear reaction

14 What is meant by a nuclear fission reaction? Give an example.

15 What is meant by nuclear fusion reaction? Give an example.

16 Name the reaction taking place in a nuclear reactor. What is a chain reaction?

17 What is a moderator in a nuclear reactor? Name the materials that can be used as moderators.

18 Give the reactions taking place in a nuclear reactor