**24 June 2013**

**TIME: 1.5 Hours —- Total Marks 50**

**Objective {3 questions carry 3 marks, all to be answered}**

**1. What’s the work done to take a charge Q on a circular voyage on an equipotential surface?**

A. Zero B. Depends on radius of circle

C. Depends on distance from center of equipotential surface D. Q/ε_{0}

**2. Rutherford’s atomic model is based on which fact**

A. Geiger Marsden scattering of α-particles suggests presence of nucleus.

B. Smith’s electrodes dipped in electrochemical material

C. Quantization of charge D. Quantization of angular momentum

**3. Half life T _{1/2} and decay constant **

**l are related as follows**

A. T_{1/2 }= (ln ½)/ l B. T _{1/2 }= e^{– }^{l} / l

C. T_{1/2} is a constant and does not depend on **l **D. T_{1/2} **=** A / (Z+A)

**Subjective {5 questions carry 5 marks, all to be answered}**

**4. Write the SI unit of electrostatic potential **

**5. If half life of radon is x hours and you have 100 Radon nuclei after what time you will be having 25 of them due to radioactive decay? **

**6. What’s the typical energy output range of Indian nuclear reactors?**

**7. Which of the following physical quantity is scalar, electric field intensity, electric potential, Dipole Moment. **

**8. Between a dipole and point charge whose potential drops faster?**

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**Long Answer {6 out of 9 questions carry 7 marks each, answer only any two from each section, Draw necessary diagrams with suitable quantities and units shown across the diagram}**

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**Section A**

**9. Use superposition principle of electric field intensity of two charges to obtain the electric field intensity E of a dipole along the dipole axis. {End-on electric field} Also use the same idea to obtain the potential at a point vertical to the dipole axis. {Broad-on potential}**

**10. Obtain the electric field intensity E of a dipole vertical to the dipole axis. {Broad-on electric field} Also obtain the potential at a point on the dipole axis. {End-on potential}**

**11. State the Coulomb’s law of interaction for two charges in vector form. Define permittivity of free space, relative permittivity of a medium and permittivity of the medium and write the relation between them. Define Electric flux and state Gauss law. Write 3 properties of electric lines of force. Write two properties of Gaussian surface. Write one property of equipotential surface **

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**Section B**

**12. Describe the principle of a nuclear reactor with a suitable diagram and write the functions of its important components. Write two aspects of Nuclear Hazard. **

**13. State Postulates of Bohr’s atomic model. Use the angular momentum quantization in stationary orbit to obtain the quantized radius ****r _{n}, speed **

**v**

_{n}and energy**E**

_{n}electron in orbits of H-atom.**14. Starting out with the law of radioactive decay derive the expression for number of nuclei at any time as a function of initial number of nuclei and decay constant. Derive the relation between half life and decay constant from this. **

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**Section C**

**15. Describe the Rutherford atomic model by explaining results of Geiger Marsden scattering experiment. Draw a PE, KE, E diagram of a Rutherford H-atom. Draw the Marsden scattering experiment plot and Gold-foil alpha-particle deflection diagram and explain each with 1 or 2 sentences. What are the drawbacks of this model? (2 is enough)**

**16. Use the Bohr’s n-th level energy -13.61/n ^{2} eV to find the energy of absorption from n=2 to n =6 state and energy of emission from n=5 to n=3 state. **

**17. Describe the Van-de-Graf generator, its principle, working and use. **