CBSE Guess > Papers > Important Questions > Class XII > 2007 > Physics > Physics (Atomic nucleus) By: Mr. Abhishek Gupta

Atomic Nucleus

Q. 1. Compare the radii of two nuclei with mass number 1 and 27.

Q. 2. Draw the graph showing the variation of binding energy per nucleon with mass number. State 2 inferences from this graph.

Q. 3. Define Impact parameter and distance of closest approach. Briefly explain the observations of Rutherford’s alpha particle scattering experiment

Q. 4. Define the term decay constant and half-life of a radioactive sample. Derive the relation b/w them

b. : How many disintegrations per second will occur in one gram of U-235 if its half-life against alpha decay is 1.42x10¹⁷s?

Q. 5. The half-life of C-14 is 5700 Years. What does it mean? Two radioactive nuclei X and Y initially contain an equal number of atoms. Their half-life is 1 hour and 2 hour respectively. Calculate the ratio of their rates of disintegration after 2 hours.

Q. 6. Draw the graph to show the variation of binding energy per nucleon with mass number of different nuclei. Calculate the binding energy per nucleon of Ca⁴⁰

Given : Mass of Ca⁴⁰ = 39.962589amu, mass of proton = 1.007825 amu, mass of neutron = 1.008665 amu

Q. 7. In a series of radioactive disintegration of ^ZX _A first an alpha particle and then a beta particle is emitted. What is the atomic and mass number of the new nucleus formed by this disintegration.

Q. 8. Show that the nuclear density is independent of mass number i.e. the nuclear density is same for all elements. What is its value?

Q. 9. Explain the stability of a nucleus in terms of n/p ratio. What happens if the n/p ratio doe not lie in the stability zone

Q. 10. What are nuclear forces. Mention 5 properties.

Q. 11. Name the reaction which takes place when a slow neutron strikes U-235 nuclei. Write the nuclear reaction involved.

Q. 12. Mention 5 properties each of alpha, beta and gamma rays. How do they affect the n/p ratio.

Q. 13. How is binding energy related to nuclear stability. Which element has the highest binding energy per nucleon and what is its value.

Q. 14. Mention 4 features of the binding energy curve.

Q. 15. What is the use of control rods in a nuclear reactor? What are they made of ? Why is heavy water used as a moderator in a nuclear reactor?

Q. 16. Complete the following nuclear reactions :

1. 7N14 (n,p)
2. 6C14 (1H1,α)
3. 8O18 (α,β)
4. 8O18 (β,α)

Q. 17. What is radioactivity? Mention the difference b/w natural and artificial radioactivity.

Q. 18. What is the difference b/w fission and fusion reaction? Give suitable examples.

Q. 19. Uranium has a half-life of 2000 years. A sample initially contains 100kg of uranium. What amount of uranium will be left after 4000 years?

Q. 20. Polonium has a half-life of 500 years. Find the following

1. Average life and disintegration constant
2. Time after which 10% of polonium will be left
3. Time in which 10% polonium would have reacted
4. Percentage of polonium left after 2500 years
5. Percentage of polonium left after 3 half-lives

Q. 21.A radioactive element X has a half-life of 100years. A sample contains 2 moles of X.

Find the following

1. Initial rate of disintegration
2. Amount of X left after 200 years
3. Rate of disintegration after 200 years

Q. 22. An element Y emits one alpha and two beta particles. What is the relation b/w the starting and the final element.

Q. 23. Define Isotopes, Isobars and isotones giving two examples of each

Q. 24. Let mass of proton = 1.007825 amu and mass of neutron = 1.008665 amu. The mass of sodium nucleus is found to be 23.05789 amu. Why is there a difference b/w the actual and the calculated mass? What is this difference called?

(b) Find the binding energy per nucleon for sodium

Q. 25. How many disintegrations per second will occur in 1kg of U-238 if its half-life against alpha decay is 1017 seconds

(b) The half-life of Uranium-238 against α-decay is 1.0 × 1017 s. What is the activity of a sample of 238 U having 25 × 1020 atoms ?

Q. 26. An element A has a half-life of 100 years while B has a half-life of 150 years. Initially a sample of 100kg has 60% A and 40% B. After what time will their concentrations be equal.

Q.27. Draw a graph showing the variation of potential energy of a pair of nucleons as a function of their separation. Indicate the regions in which nuclear force is

1. attractive, and
2. repulsive.

(b) Write two characteristic features of nuclear force which distinguish it from the Coulomb force.

Q. 28. Show that the decay ratio 'R' of a sample of a radionuclide is related to the number of radioactive nuclei 'N' at the same instant by the expression R = λN.

Q. 29. A star converts all its hydrogen to helium achieving 100% helium composition. It then converts helium to carbon via the reaction

2He⁴ + 2He⁴ + 2He⁴ --> ₆C ¹² + 7.27MeV

The mass of the star is 5.0 x 10³²Kg and it generates energy at the rate of 5.0 x 10³⁰ Watt. How long will it take to convert all the helium to carbon.

Q. 30. Define mass number (A) of an atomic nucleus. Assuming the nucleus to be spherical, give the relation between the mass number (A) and the radius (R) of the nucleus. Calculate the density of nuclear matter. Radius of nucleus of = 1.1 × 10—5Å. What is the ratio of the order of magnitude of density of nuclear matter and density of ordinary matter .