CBSE Class 12 Physics Nuclei Worksheet

CBSE Class 12 Physics Nuclei Worksheet Set A

Question. If 1 mg of U²³⁵ is completely annihilated, the energy liberated is
(a) 9 × 10¹⁰ J
(b) 9 × 10¹⁹ J
(c) 9 × 10¹⁸ J
(d) 9 × 10¹⁷ J

Answer: A

Question. A heavy nucleus having mass number 200 gets disintegrated into two small fragments of mass number 80 and 120. If binding energy per nucleon for parent atom is 6.5 MeV and for daughter nuclei is 7 MeV and 8 MeV respectively, then the energy released in the decay is X × 110 MeV. Find the value of X.
(a) 3
(b) 4
(c) 2
(d) 1

Answer: C

Question. The mass defect in a particular nuclear reaction is 0.3 grams. The amount of energy liberated in kilowatt hour is (Velocity of light = 3 × 10⁸ m/s)
(a) 1.5 × 10⁶
(b) 2.5 × 10⁶
(c) 3 × 10⁶
(d) 7.5 × 106

Answer: S

Question. A radioactive nuclide is produced at the constant rate of n per second (say, by bombarding a target with neutrons).
The expected number N of nuclei in existence t seconds after the number is N₀ is given by 

Answer: C

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: B

Question. The activity of a radioactive sample is measured as N₀ counts per minute at t = 0 and N₀/e counts per minute at t = 5 minutes. The time (in minutes) at which the activity reduces to half its value is
(a) loge 2 / 5
(b) 5/loge 2
(c) 5 log 10²
(d) 5 loge 2

Answer: D

Question. The radioactivity of a sample is R₁ at a time T₁ and R₂ at a time T₂. If the half-life of the specimen is T, the number of atoms that have disintegrated in the time (T₁ – T₂) is proportional to
(a) (R₁T₁ – R₂T₂₎
(b) (R₁ – R₂)
(c) (R₁ – R₂)/T
(d) (R₁ – R₂) T

Answer: D

Question. The mass and energy equivalent to 1 amu are respectively
(a) 1.67 × 10^–27 gm, 9.30 MeV
(b) 1.67 × 10^–27 kg, 930 MeV
(c) 1.67 × 10^–27 kg, 1 MeV
(d) 1.67 × 10^–34 kg, 1 MeV

Answer: B

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

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) 3N₀
(b) 9N₀/2
(c) 5N₀/2
(d) 2N₀ 

Answer: B

Question. The activity of a radioactive sample is measured as 9750 counts per minute at t = 0 & 975 counts per minute at T = 5 minutes. The decay constant is approximately.
(a) 0.922 per minutes
(b) 0.691 per minutes
(c) 0.461 per minutes
(d) 0.230 per minutes

Answer: C

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. 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. 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. If the distance between nuclei is 2 × 10^–13 cm, the density of nuclear material is
(a) 3.21 × 10^–12 kg/m³
(b) 1.6 × 10^–3 kg/m3
(c) 2 × 10⁹ kg/m3
(d) 1 × 10¹⁷ kg/m³

Answer: D

Question. A radioactive element X converts into another stable element Y. Half life of X is 2 hrs. Initially only X is present. After time t, the ratio of atoms of X and Y is found to be 1 : 4, then t in hours is
(a) 2
(b) 4
(c) between 4 and 6
(d) 6

Answer: C

Question. The half life of the radioactive substance is 40 days. The substance will disintegrate completely in
(a) 40 days
(b) 400 days
(c) 4000 days
(d) infinite time

Answer: D

Question. An electron is
(a) hadron
(b) baryon
(c) a nucleon
(d) a lepton.

Answer: D

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 of 1 : 7 in a sample of a the given rock. The age of the rock is estimated to be
(a) 60 years
(b) 80 years
(c) 100 years
(d) 40 years

Answer: A

Question. Fraction of tritium left after 150 years (half life of tritium is 12.5 years) is
(a) 1/ 1024
(b) 1/2048
(c) 1/4096
(d) 1/8192

Answer: C

Question. Half lives for α and β emission of a radioactive material are 16 years and 48 years respectively. When material decays giving α and β emission simultaneously, time in which 3/ 4^th material decays is
(a) 29 years
(b) 24 years
(c) 64 years
(d) 12 years

Answer: B

Question. The volume of a nucleus is directly proportional to
(a) A
(b) A³
(c) √A
(d) A1/3

Answer: A

Question. The half-life of radioactive Radon is 3.8 days. The time at the end of which (1/20)th of the Radon sample will remain undecayed is (given log₁₀e = 0.4343)
(a) 13.8 days
(b) 16.5 days
(c) 33 days
(d) 76 days

Answer: B

Question. The decay constant of radium is 4.28 × 10^–4 per year. Its half life will be
(a) 2000 years
(b) 1240 years
(c) 63 years
(d) 1620 years

Answer: D

Question. The nucleus

after two successive β– decay will give

Answer: D

Question. Suppose we consider a large number of containers each containing initially 10000 atoms of a radioactive material with a half life of 1 yr. After 1 year,
(a) all the containers will have 5000 atoms of the material
(b) all the contains will conatin the same number of atoms of the material but that number will only be approximately 5000
(c) the containers will in general have different numbers of the atoms of the material but their average will be close to 5000
(d) none of the containers can have more than 5000 atoms.

Answer: C

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. 

Answer: A

Question. When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom
(a) do not change for any type of radioactivity
(b) change for α and β-radioactivity but not for gradioactivity
(c) change for α-radioactivity but not for others
(d) change for β-radioactivity but not for others

Answer: B

Question. Mx and My denote the atomic masses of the parent and the daughter nuclei respectively in radioactive decay. The Q – value for a β^– decay is Q₁ and that for a β⁺ decay is Q₂. If m_e denotes the mass of an electron, then which of the following statements is correct?
(a) Q₁ = (M_x – M_y) c² and Q₂ = [M_x – M_y – 2me] c²
(b) Q1 = (M_x – M_y) c² and Q₂ = (M_x – M_y) c²
(c) Q₁ = (M_x – M_y – 2m_e) c² and Q₂ = (M_x – M_y + 2c_e) c²
(d) Q₁ = (M_x – M_y + 2m_e) c² and Q₂ = (M_x – M_y + 2 m_e)c2

Answer: A

Question. Tritium is an isotope of hydrogen whose nucleus triton contains neutrons and 1 proton. Free neutrons decay into p + e̅ + n̅ . If one of the neutrons is Triton decays, it would transform into He³ nucleus. This does not happen. This is because
(a) Triton energy is less than that of a He³ nucleus
(b) The electron created in the beta decay process cannot remain in the nucleus
(c) both the neutrons in triton have to decay simultaneously resulting in a nucleus with 3 protons, which is not a He3 nucleus.
(d) free neutrons decay due to external perturbations which is absent in triton nucleus

Answer: A

Question. The gravitational force between a H-atom and another particle of mass m will be given by Newton's law 

Answer: B

Question. In a fission reaction 

the binding energy per nucleon of X & Y is 8.5 MeV. Whereas of ²³⁶U is 7.6 MeV. The total energy liberated will be about
(a) 2000 MeV
(b) 200 MeV
(c) 2 MwV
(d) 200 KeV

Answer: B

Question. The half life of a radioactive nucleus is 50 days. The time interval (t₂ – t₁) between the time t₂ when 2/3 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. Heavy stable nuclei have more neutrons than protons. this is because of the fact that
(a) neutrons are heavier than protons
(b) electrostatic force between protons are repulsive
(c) neutrons decay into protons through beta decay
(d) nuclear force between neutrons are weaker than that between protons

Answer: B

Question. The binding energies per nucleon for a deuteron and an α-particle are x₁ and x₂ respectively. What will be the energy Q released in the reaction ₁H² + ₁H² → ₂He⁴ + Q
(a) 4(x₁ + x₂)
(b) 4(x₂ – x₁)
(c) 2(x₁ + x₂)
(d) 2(x₂ – x1)

Answer: B

Question. A duetron strikes ₈O¹⁶ nucleus with subsequent emission of alpha particle. Identify the nucleus so produced 
(a) ₃Li⁷
(b) ₅B¹⁰
(c) ₇N¹³
(d) ₇N¹⁴

Answer: D

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 of 1 : 7 in a sample of a the given rock. The age of the rock is estimated to be 
(a) 60 years
(b) 80 years
(c) 100 years
(d) 40 years

Answer: A

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

Answer: C

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

Answer: D

Question. After 150 days, the activity of a radioactive sample is 5000 dps. The activity becomes 2500 dps after another 75 days. The initial activity of the sample is
(a) 20000 dps
(b) 40000 dps
(c) 7500 dps
(d) 10000 dps

Answer: A

Question. The more readily fissionable isotope of uranium has an atomic mass of
(a) 234
(b) 235
(c) 236
(d) 238

Answer: B

DIRECTIONS : Each of these question contains two statements: Statement-1 (Assertion) and Statement-2 (Reason). Answer these questions from the following four options.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement -1
(b) Statement-1 is True, Statement -2 is True; Statement-2 is NOT a correct explanation for Statement - 1
(c) Statement-1 is True, Statement- 2 is False
(d) Statement-1 is False, Statement -2 is True

Question. Statement- 1 : Radioactivity of 10⁸ undecayed radioactive nuclei of half life of 50 days is equal to that of 1.2 × 10⁸ number of undecayed nuclei of some other material with
half life of 60 days.
Statement- 2 : Radioactivity is proportional to half-life.

Answer: C

Question. Statement- 1 : The ionising power of β-particle is less compared to α-particles but their penetrating power is more.
Statement- 2 : The mass of β-particle is less than the mass of α-particle.

Answer: B

Question. Statement- 1: The binding energy per nucleon, for nuclei with atomic mass number A > 100, decrease with A.
Statement- 2 : The forces are weak for heavier nuclei.

Answer: C
 

              Very Short Answer

Q1)       What is mass defect?

Q2)       What is red giant?

Q3)       How can we get the accurate measurement of the atomic masses?

Q4)       What kind of source of energy output in the interior of stars?

Q5)       Define isotopes?

              Short Answer

Q6)       What do you understand by the law of radioactive decay?

Q7)       What do you mean by nuclear holocaust?

Q8)       Define atomic mass?

Q9)       What do you mean by the term thermonuclear fusion?

Q10)     What do you understand by the term nuclear energy?

              Long Answer

Q11)     Explain about radioactivity and its types?

Q12)     State the difference between isotopes and isobars?

Q13)     Write short note on nuclear force?

Q14)     Write short note on mass energy and nuclear binding energy?

Q15)     State the difference between nuclear fission and nuclear fusion?