Answer: Question 6. Define the activity of a given radioactive substance. Nuclear fusion : The binding energy per nucleon is small for light nuclei, i.e., they are less stable. Obtain the relation \(\mathbf{N}=\mathbf{N}_{0} e^{-\lambda t}\) for a sample of radioactive material having decay constant λ, where N is the number of nuclei present at constant λ. Nuclear forces are charge independent. Answer: Question 16. (Comptt. So, the Mass number of A4 is 182 Answer: Nuclear forces are dependent on spin. Answer: The proton (denoted by p) has a charge +e and a mass, which is approximately 1840 times larger than the electron mass. (b) (i) When we move from heavy nuclei region to middle region, we find that there will be a gain in overall binding energy and hence release of energy. What is the ratio of their nuclear densities? Do the elements follow a certain pattern? The atomic nucleus generally exists in the lowest energy state also known as ground… When a β-particle is emitted from a nucleus then its neutron-proton ratio (a) increases (b) … These... Nuclear Charge: The nucleus comprises of protons and … Atomic number: - Atomic number constitutes the total number of protons which are present in the nucleus of that atom. Answer: The graph indicates that the attractive force between the two nucleons is strongest at a separation r0 = 1 fm. (i) Why is the binding energy per nucleon found to be constant for nuclei in the range of mass number (A) lying between 30 and 170? Nuclear forces are strongest forces in nature. This force can exist between … It is denoted by ‘A’. Question 60. Here d is deutron. 3. Mass Energy Relation and Mass Defect 8. (i) (a) The mass defect of a nucleus equals the difference between the total mass of its constituents and the mass of the nucleus itself. (i) Nuclear force between two nucleons falls rapidly to zero as their distance is more than a few femtometres. I bequerel = 1 decay per second, Question 39. In every atom, the positive charge and mass are densely concentrated at the centre of the atom forming its nucleus. We can define nuclear force as: The nuclear force is the force that binds the protons and neutrons in a nucleus together. Greater binding energy of the product nuclei results in the liberation of energy. This indicates that energy can be released when two lighter 4. Short-range force Calculate the energy Q released per fission in MeV. It is this potential energy which holds the nucleons together in the nucleus. If you are at an office or shared network, you can ask the network administrator to run a scan across the network looking for misconfigured or infected devices. unit. Nuclei Class 12 Notes Chapter 13. Two nuclei have mass numbers in the ratio 8:125. Draw a plot of potential energy of a pair of nucleons as a function of their separations. (i) becquerel is the SI unit of ‘activity’ of a nuclear sample. Answer: Write the relationship between the size and the atomic mass number of a nucleus. Concepts of Physics Part 2, Numerical Problems with their solutions, Short Answer Solutions for Chapter 46 - The Nucleus from the latest edition of HC Verma Book. (iii) Nuclear Size The radius of the nucleus R ∝ A 1/3 Answer: Nuclear force is one of the four fundamental forces of nature, the others being gravitational and electromagnetic forces. (Comptt. Discovery of neutron by Chadwick. Basic Properties of Neutron • mn = 1.00866 u = 1.6749 × 10 ‒27 kg • A free neutron, unlike a free proton, is unstable. (b) Draw a plot of BE/A versus mass number A for 2 ≤ A ≤ 170. (c) When a nucleus (X) undergoes β-decay, and transforms to the nucleus (Y), does the pair (X, Y) form isotopes, isobars or isotones? What is the ratio of their nuclear densities? Two nuclei have mass numbers in the ratio 1: 8. For separation (r) ≤ 0.8 fermi Factors Affecting Stability of Nucleus Question 14. Identify and compare the three types of decay: Alpha, Beta and Gamma. (a) In all types of nuclear reactions, the law of conservation of number of nucleons is followed. (ii) repulsive. Question 8. Heat exchanger: Here water is converted into high pressure steam using the heat energy of the coolant and send to the turbines which rotates and produces electricity. How long will it take the activity to reduce to 3.125% of its original value? Delhi 2012) (i) mass of neutrino is extremely small; Answer: What are these numbers for A4? (b) β-decay. (b) Suppose a radioactive sample contains N0 nuclei at time t = 0. (Delhi 2008) (c) Why is it found experimentally difficult to detect neutrinos? Explain. They are called nucleons. Two nuclei have mass numbers in the ratio 8:125. (Delhi 2016) Draw a plot of potential energy of a pair of nucleons as a function of their separation. The emission of β-particle from an atom will change it into a new atom whose atomic number is increased by one without changing its mass number. The mass number and atomic number of A are 180 and 72 respectively. (b) Binding energy per nucleon of the daugher nuclei, in both processess, is more than that of the parent nuclei. The property that a given nucleon influences only nucleons close to it is also referred to as saturation property of the nuclear force. Mark the regions where the nuclear force is Class 12 Physics Nuclei: Composition of Nucleus: Composition of Nucleus. heavier nuclei are less stable. It constitutes two different elementary particles known as protons and neutrons. Performance & security by Cloudflare, Please complete the security check to access. (Delhi 2014) Sep 22, 2020 - NCERT Textbook - Nuclei Class 12 Notes | EduRev is made by best teachers of Class 12. CBSE Class 12 Physics Revision Notes for Chapter 13 - Nuclei × Sorry!, This page is not available for now to bookmark. (b) In the reactions given below : (c) In Beta decay a neutron breaks into a proton, electron and neutrino as Question 53. This mass is received from the binding energy of the nucleus. (All India 2009) The series can be shown as below: Answer: Answer: Question 20. Question 47. (i) positive and Calculate the energy release in MeV in the deuterium-tritium fusion reaction : Thus the density of nucleus is a constant, independent of A, for all nuclei. If both the number of protons and neutrons in a nuclear reaction is conserved, in what way is mass converted into energy (or vice verse)? (iii) The nuclear force between neutron- neutron, proton-neutron and proton-proton is approximately the same. although number of nucleons is conserved, yet energy is released. Answer: The number of protons and neutrons in a nuclear reaction are conserved but the total mass is not conserved. If a nucleon can have maximum of P neighbours within the range of nuclear force, its binding energy would be proportional to ‘P’ Thus on increasing ‘A’ by adding nucleons binding energy will remain constant. Nuclear fission : Binding energy per nucleon is smaller for heavier nuclei than the middle ones i.e. It states that “the number of atoms disintegrated per second at any instant is directly proportional to the number of radioactive atoms actually present at that time.” Let N0 be the total number of atoms present at time t = 0 (initially) (i) Nuclear forces are short ranged. (b) Use this graph to explain the release of energy in both the processes of nuclear fusion and fission. Depict in the plot the number of undecayed nuclei at But it absorbs neutrons at a fast rate via reaction : (ii) The binding energy per nucleon of the parent nucleus is less than those of the two daughter nuclei. Physics Notes for Class 12 Chapter 13 Nuclei Nucleus The entire positive charge and nearly the entire mass of atom is concentrated in a very small space called the nucleus of an atom. In this section, we will discuss this force in detail. 4. Two important conclusions : All India 2017) Answer: Question 10. Calculate average mass. (i) mass of neutrino is extremely small; (Comptt. Their half lives are 3h and 4h respectively. (b) Explain. As ordinary water contains hydrogen atoms (of mass nearly that of neutrons), so it can be used as a moderator. The nuclear force does not depend on the electric charge. Write the expression for the law of radioactive decay in terms of the activity of a given sample. Answer: Answer: protons and neutrons. The nuclear binding force has to dominate over the Coulomb repulsive force between protons inside the nucleus. All India 2017) How is it related with its binding energy? Students can solve NCERT Class 12 Physics Nuclei MCQs Pdf with Answers to know their preparation level. It is the reciprocal of the time interval in which the number of active nuclei in a radioactive sample reduces to 1/e times of its initial nuclei. Parameter of Nucleus (i) Radius of nucleus It is proportional to the cube root of the mass number of element. • Answer: Answer: Question 7. (Delhi 2008) (All India 2008) Two radioactive samples, X, Y have the same number of atoms at t = 0. 1. Protons are positively charged particles which are present inside the nucleus and neutrons are neutral as they don’t have any charge. Nuclear forces are strongest forces in nature. Write two characteristic features of nuclear force. Answer: (All India 2009) What is the ratio of their nuclear densities? NUCLEAR FUSION In fusion two light nuclei combine to become a heavier nuclei releasing energy. The number of nuclei undergoing decay per unit time, at any instant is proportional to number of nuclei in the sample at that instant. What is the ratio of their nuclear densities? The SI unit for activity is becquerel (Bq). State the reason, why heavy water is generally used as a moderator in a nuclear reactor. Question 19. Learn in detail topic atomic masses and composition of nucleus, helpful for cbse class 12 phyiscs chapter 13 nuclei, neet and jee exam preparation. You may need to download version 2.0 now from the Chrome Web Store. In a hydrogen molecule, there are two protons and two electrons. Question 55. unit is bequerel I bequerel = 1 decay per second, Question 38. So when two light nuclei combine to form a heavier nucleus, the higher binding energy per nucleon of the latter results in the release of energy. (c) In Beta decay a neutron breaks into a proton, electron and neutrino as The strong forces of attraction which hold together the nucleons (neutrons and protons) in the tiny nucleus of an atom are called nuclear forces. Neutrons produced during fission get slowed if they collide with a nucleus of the same mass. (b) Draw a plot of potential energy between a pair of nucleons as a function of their separation. Two characteristic features of nuclear forces : (b) Draw a plot of potential energy of a pair of nucleons as a function of their separation. Question 23. (a) The constancy of the binding energy in the range 30 < A < 170 is a consequence of the fact that the nuclear force is short ranged. unit. You will also learn about discovery of neutrons, atomic number, … Question 57. Conclusions : 1. Question 17. This is what happens in nuclear fission which is the basis of the atom bomb. Nuclear fission : Binding energy per nucleon is smaller for heavier nuclei than the middle ones i.e. #physics #NuclearMass #NuclearSize Physics Class-12 Thanks for watching this video. Write any two characteristic features of nuclear forces. Since nuclear density is independent of the mass number, the ratio of nuclear densities will be 1:1. Properties of the Nucleus (i) Nucleus is a small, heavy, positively charged portion of the atom and located at the centre of the atom. Question 54. (Comptt All India 2009). Question 24. (b) Plot a graph showing the variation of potential energy of a pair of nucleons as a function of their separation. Question 5. Its S.I. All India 2014) nuclei fuse together to form heavy nucleus/nuclear fusion. (ii) Similarly, when we move from lighter nuclei to heavier nuclei, we find that there will be gain in overall binding energy and hence release of energy. Nuclei Class 12 Physics MCQs Pdf. Answer: Question 56. Answer: (Delhi 2016) (Delhi 2009) All India 2012) These rays were called cathode rays. A radio active nucleus ‘A’ undergoes a series of decays according to the following scheme: According to Greater binding energy of the product nuclei results in the liberation of energy. (i) attractive and R o = proportionality constant = 1.4 x l0 – 13 rn= 1.4 x 10 – 15 cm. The lost mass (= ∆m) known as ‘mass defect’, gets converted into energy as per the relation E = (∆m)c2 (c is the velocity of light). The binding energy of nucleons in Y and Z is 8.5 MeV per nucleon. The nucleus has 2 primary functions: It is responsible for storing the cell’s hereditary material or the DNA. 2. Answer: Question 58. Answer: Compare the rates of disintegration of the two nuclei after 12 hours. Answer the following, giving reasons: This explains constancy of the binding energy per nucleon for large-size nucleus. It is found experimentally difficult to detect neutrinos in nuclear P-decay, because of two reasons : (a) The activity of a radioactive nucleus equals its decay rate (or number of nuclei decaying per unit time). (a) Decay constant. (i) Define ‘activity’ of a radioactive material and write its S.I. Click here. (ii) Plot a graph showing variation of activity of a given radioactive sample with time. (iii) Neutrinos are chargeless and massless particles, whose interaction with other particles is almost negligible. (ii) negative. Question 8. (Delhi 2009) Control rod or cadmium rod. When a heavier nucleus splits into the lighter nuclei, the B.E./nucleon changes (increases) from about 7.6 MeV to 8.4 MeV. Free PDF download of Class 12 Physics revision notes & short key-notes for Chapter 13 - Nuclei to score high marks in exams, prepared by expert Physics teachers from latest edition of CBSE(NCERT) books. (Comptt. Physics MCQs for Class 12 Chapter Wise with Answers PDF Download was Prepared Based on Latest Exam Pattern. Answer: Question 6. Answer: Question 9. (All India 2016) Question 12. Energy equivalent of mass defect is released. Question 45. Question 43. Complete the following nuclear reactions : Complete the following nuclear reactions : Name the absorbing material used to control the reaction rate of neutrons in a nuclear reactor. Why? Nuclear density is independent of mass number, so the ratio will be 1 : 1. Define the activity of a radionuclide. The proton is the nucleus of the simplest atom with Z = 1, viz. Question 25. Question 44. Delhi 2014) (Delhi 2009) (i) The force is attractive and sufficiently strong to produce a binding energy of a few MeV per nucleon. It is responsible for coordinating many of the important cellular activities such as protein synthesis, cell division, growth and a host of other important functions. (All India 2012) though the conserved on both sides of the reaction, yet the energy is released. Detection of neutrinos is difficult because they are chargeless and have either no or low mass. In the behaviour of hydrogen molecule, the nuclear force between these protons is always neglected. (a) The mass of a nucleus in its ground state is always less than the total mass of its constituents – neutrons and protons. 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In this video lecture you will learn about nucleus in this lecture, constituents of nucleus, size of nucleus, nuclear force, binding energy and mass defect. Answer: Delhi 2017) (iii) Nucleus contains neutrons and protons, and hence these … 1. State the law of radioactive decay. unit. (a) The activity of a radioactive source is measured by the rate of disintegration of the source. Two nuclei have mass numbers in the ratio 2 : 5. Write the relation between half life and decay constant of a radioactive nucleus. Nucleus is located in the centre of the atom and it is positively charged whereas electrons negatively charged and revolve around the nucleus in the orbits. If a nucleon can have a maximum of p neighbours within the range of nuclear force, its binding energy would be proportional to p. Since most of the nucleons in a large nucleus reside inside it and not on the surface, the change in binding energy per nucleon would be small. 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