# Physics for XII, ICSE. Preparatory Test for Quarterly. Reply

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/ε0

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.  T1/2 = (ln ½)/ l                                                           B. T 1/2 = el / l

C. T1/2 is a constant and does not depend on l        D. T1/2 = 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?

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}

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

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 rn, speed vn and energy En 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.

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/n2 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.