CBSE Class 12 Physics Nuclei Worksheet Set A

1. Give a point of evidence that most of the space in an atom is empty. 

2. What are isotopes? Give an example. 

3. Name the isotope of Hydrogen which do not occur naturally? 

4. Who discovered neutron? In which year he was awarded the noble prize. 

5. Discuss about the stability of a free neutron. 

6. What are isobars? Give an example 

7. What are isotones? Give an example. 

8. What is the relationship existing between the radius(R) of a nucleus and mass number A? 

9. Given the mass of iron nucleus as 55.85amu and A=56, find the nuclear density?

10. Give the equation of mass-energy equivalence. Also Calculate the energy equivalent of 1 g of substance. 

11 What is mass defect Give the formula for finding mass defect. What is the corresponding energy related to the mass defect. 

12 Draw a graph showing the variation of binding energy per nucleon as a function of mass number. Also give the important features of it. Give the important conclusions from the graph

13 Draw a graph showing the variation of potential energy of a pair of nucleons as a function of their separation. Give any two important conclusions from the graph.

14 What are the properties of nuclear forces?

15 Who discovered Radioactivity?

16 What is meant by radioactive decay? How many types of radioactive decay are there? What are they?

17 Derive the expression 𝑁(𝑡)=𝑁0 𝑒−𝜆𝑡

Important Questions for NCERT Class 12 Physics Nuclei 

Question. Which one of the following pairs of nuclei are isotones?
(a) 34Se74, 31Ga71
(b) 38Sr84, 38Sr86
(c) 42Mo92, 40Zr92
(d) 20Ca40, 16S32 

Answer  A

Question. A nucleus represented by the symbol Z AX has
(a) Z neutrons and A – Z protons
(b) Z protons and A – Z neutrons
(c) Z protons and A neutrons
(d) A protons and Z – A neutrons 

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. 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. The mass number of a nucleus is
(a) always less than its atomic number
(b) always more than its atomic number
(c) sometimes equal to its atomic number
(d) sometimes less than and sometimes more than its atomic number 

Answer  C

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

Answer  C

Question. The constituents of atomic nuclei are believed to be
(a) neutrons and protons
(b) protons only
(c) electrons and protons
(d) electrons, protons and neutrons 

Answer  A

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 ₁₃²⁷Al has a nuclear radius of about 3.6 fm, then ₃₂¹²⁵Te 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 ₄⁹Be. The number of nucleons in Ge are
(a) 72
(b) 73
(c) 74
(d) 75 

Answer  A

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 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. What is the respective number of a and b particles emitted in the following radioactive decay?
²⁰⁰X₉₀ → ¹⁶⁸Y₈₀
(a) 8 and 8
(b) 8 and 6
(c) 6 and 8
(d) 6 and 6

Answer  B

Question. After 1a and 2b-emissions
(a) mass number reduces by 6
(b) mass number reduces by 4
(c) mass number reduces by 2
(d) atomic number remains unchanged

Answer  B,D

Question. The count rate of a Geiger Muller counter for the radiation of a radioactive material of half-life of 30 minutes decreases to 5 second–1 after 2 hours.
The initial count rate was
(a) 80 second^–1
(b) 625 second^–1
(c) 20 second^–1
(d) 25 second^–1 

Answer  A

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. The mass of a-particle is
(a) less than the sum of masses of two protons and two neutrons
(b) equal to mass of four protons
(c) equal to mass of four neutrons
(d) equal to sum of masses of two protons and two neutrons 

Answer  A

Question. The half life of radium is 1600 years. The fraction of a sample of radium that would remain after 6400 years
(a) 1/4
(b) 1/2
(c) 1/8
(d) 1/16 

Answer  D

Question. The nucleus ₆C¹² absorbs an energetic neutron and emits a beta particle (b). The resulting nucleus is
(a) ₇N¹⁴
(b) ₇N¹³
(c) ₅B¹³
(d) ₆C¹³ 
Answer  B

Question. A radioactive sample with a half life of 1 month has the label : ‘Activity = 2 micro curies on 1 – 8 – 1991’.
What would be its activity two months earlier?
(a) 1.0 micro curie
(b) 0.5 micro curie
(c) 4 micro curie
(d) 8 micro curie

Answer  D

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

Answer  A

Question. In each fission of 92U235 releases 200 MeV, how many fissions must occur per second to produce power of 1 kW ? 
(a) 1.25 × 10¹⁸
(b) 3.125 × 10¹³
(c) 3.2 × 10¹⁸
(d) 1.25 × 10¹³

Answer  B

Question. The function of heavy water in a nuclear reactor to
(a) slow down the neutrons 
(b) increase the neutrons
(c) stop the electrons
(d) none of these

Answer  A

Question. Which one of the following has the highest neutrons ratio ?
(a) 92U235
(b) 8O16
(c) 2He4
(d) 26Fe56

Answer  A

Question. A radioactive substance decays to 1/16th of its initial activity in 40 days. The half-life of the radioactive substance expressed in days is
(a) 2.5
(b) 5 
(c) 10
(d) 20

Answer  C

Question. Nuclear fusion is possible 
(a) only between light nuclei
(b) only between heavy nuclei
(c) between both light and heavy nuclei
(d) only between nuclei which are stable against b-decay

Answer  A

Question. Radioactive nuclei that are injected into a potient collected at certain sites within its body, undergoing radioactive decay and emitting electromagnetic radiation. These radiations can then be recorded by a detector. This procedure provides an important diagnostic tools called
(a) Gamma camera 
(b) CAT can
(c) Radiotracer technique
(d) Gamma ray spectroscopy

Answer  C

Question. In a material medium, when a positron meets an electron both the particles annihilate leading to the emission of two gamma ray photons. This process forms the basis of an important diagnostic procedure called 
(a) MRI
(b) PET
(c) CAT
(d) SPECT

Answer  B

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

Answer  B

Question. The reaction responsible for the production of light energy from the sun will be: 
(a) fission
(b) fusion
(c) nuclear
(d) none of these

Answer  B

Question. Carbon dating is best suited for determining the age of fossils if their age in years is of the order of
(a) 10³
(b) 10⁴
(c) 10⁵
(d) 10⁶

Answer  B

Question. When an electron-positron pair annihilates, the energy released is about 
(a) 0.8 × 10^–13 J
(b) 1.6 × 10^–13 J
(c) 3.2 × 10^–13 J
(d) 4.8 × 10^–13 J

Answer  B

Question. A radioactive material has half-life of 10 days.
What fraction of the material would remain after 30 days ? 
(a) 0.5
(b) 0.25
(c) 0.125
(d) 0.33

Answer  C

Question. The operation of a nuclear reactor is said to be critical, if the multiplication factor (K) has a value
(a) 1
(b) 1.5 
(c) 2.1
(d) 2.5

Answer  A

Question. If Alpha, Beta and Gamma rays carry same momentum, which has the longest wavelength
(a) Alpha rays 
(b) Beta rays
(c) Gamma rays
(d) None, all have some wavelength

Answer  D

Question. What is the amount of energy released by deuterium and tritium fusion? 
(a) 60.6 eV
(b) 123.6 eV
(c) 17.6 eV
(d) 28.3 eV

Answer  C

Question. Calculate power output of ₂₃₅ ⁹² U reactor, if it takes 30 days to use up 2 kg of fuel, and if each fission gives 185 MeV of useable energy.
Avogadro's number = 6 × 10²³ /mol? 
(a) 56.3 MW
(b) 60.3 MW
(c) 58.3 MW
(d) 54.3 MW

Answer  C

Question. A radioactive material decays by simultaneous emission of two particles with respective halflives 1620 and 810 years. The time, in years, after   which one-fourth of the material reamins is
(a) 1080
(b) 2430 
(c) 3240
(d) 4860

Answer  A

Question. If the binding energy per nucleon of a nuclide is high then 
(a) It should be abundantly available in nature
(b) It will decay instantly
(c) It will have a large disintegration constant
(d) It will have a small half-life.

Answer  A

Question. Activity of a radioactive sample decreases to (l/3)rd of its original value in 3 days. Then, in 9 days its activity will become 
(a) (1/27) of the original value
(b) (1/9) of the original value
(c) (1/18) of the original value
(d) (1/3) of the original value

Answer  A

Assertion and Reason

Note: Read the Assertion (A) and Reason (R) carefully to mark the correct option out of the options given below:
a. If both assertion and reason are true and the reason is the correct explanation of the assertion.
b. If both assertion and reason are true but reason is not the correct explanation of the assertion.
c. If assertion is true but reason is false.
d. If the assertion and reason both are false.
e. If assertion is false but reason is true.

Question. Assertion: The half life of radioactive sample is T. It will decay to 1/16 of its initial value in a time 8T.
Reason: The half life of a radioactive sample is the time in which half of the number of nuclei decay.
Answer : D

Question. Assertion: The binding energy of deuteron (²₁H) is 1.15 MeV per nucleon and an alpha particle (⁴₂He) has a binding energy of 7.1 MeV per nucleon. Then in the reaction ²₁H + ²₁H → ⁴₂He +Q , the energy Q released is 23.8 MeV.
Reason: Total energy is conserved in a nuclear reaction.
Answer : A

Question. Assertion: The mass of a nucleus can be either less than or more than the sum of the masses of nucleons present in it.
Reason: The whole mass of the atom is considered in the nucleus.
Answer : E

Question. Assertion: All the radioactive elements are ultimately converted in lead.
Reason: All the elements above lead are unstable.
Answer : C

Question. Assertion: Amongst alpha, beta and gamma rays, α- particle has maximum penetrating power.
Reason: The alpha particle is heavier than beta and gamma rays.
Answer : D

Question. Assertion: It is not possible to use ³⁵Cl as the fuel for fusion energy.
Reason: The binding energy of n ³⁵Cl is too small.
Answer : C

Question. Assertion: The mass of β-particles when they are emitted is higher than the mass of electrons obtained by other means.
Reason: β-particle and electron, both are similar particles.
Answer : B

Question. Assertion: A nucleus X, initially at rest, decays into a nucleus Y with the emission of an α- particle and energy Q is released. If m is the mass of an alpha particle and M that of nucleus Y, the energy of the emitted α- particle will be Ea = QM/(M - m)
Reason: Momentum and energy are conserved in the decay process.
Answer : D

Question. Assertion: The ionising power of β-particle is less compared to α-particles but their penetrating power is more.
Reason: The mass of β-particle is less than the mass of α- particle.
Answer : B

Question. Assertion: The distance of the closest approach of an alpha particle fired at a nucleus with momentum p is r₀. The distance of the closest approach when the alpha particle is fired at the same nucleus with momentum 2p will be r₀/2.
Reason: The distance of closest approach from a given target element is inversely proportional to the kinetic energy of the incident particle.
Answer : S

Question. Assertion: 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
Reason: Radioactivity is proportional to half-life.
Answer : C

Question. Assertion: Fragments produced in the fission of U²³⁵ are radioactive.
Reason: The fragments have abnormally high proton to neutron ratio.
Answer : C

Question. Assertion: Electron capture occurs more often than positron emission in heavy elements.
Reason: Heavy elements exhibit radioactivity.
Answer : B

Question. Assertion: ⁹⁰Sr from the radioactive fallout from a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of the production of red blood cells.
Reason: The energetics β-particles emitted in the decay of ⁹⁰Sr damage the bone marrow.
Answer : A

Match the Column

Question. Some laws/processes are given in Column I. Match these with the physical phenomena given in Column II:
           Column I                                     Column II
(A) Nuclear fusion                            1. Converts some matter into energy
(B) Nuclear fission                           2. Generally possible for nuclei with low atomic number
(C) β − decay                                   3. Generally possible for nuclei with higher
(D) Exothermic nuclear reaction      4. Essentially proceeds by weak nuclear forces
a. A→1,2; B→1,3; C→1,4; D→1,2,3
b. A→1; B→1,2; C→1,4; D→1,2,3
c. A→1,2; B→1,3; C→4; D→1,3
d. A→2; B→1,3; C→1,4; D→2,3
Answer : A

Question. Some laws/processes are given in Column I. Match these with the physical phenomena given in Column II:

a. A→1,2; B→1,3; C→4; D→3
b. A→1,2; B→1,3; C→1,4; D→1,2,3
c. A→1; B→1,2; C→1,4; D→1,2,3
d. A→1,3; B→1,2,4; C→1; D→2
Answer : A

Integer

Question. The intensity of gamma radiation from a given source is I.
On passing through 27 mm of lead, it is reduced to I/8.
The thickness of lead which will reduced the intensity to I/2 will be?
Answer : 9

Question. The half life of a freshly prepared radioactive sample is 2h. If the sample emits radiation of intensity, which is 16 times the permissible safe level, then the minimum time taken after which it would be possible to work safely with source is?
Answer : 8