Bharathiar University 2003 M.Sc Physics Electromagnetic Theory and Electrodynamics - Question Paper
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Beg, No,:
(For the candidates admitted from 2002 and onwards) M.Se. DEGREE EXAMINATION, NOVEMBER 2003. Second Semester Part III Physics
Paper V ELECTROMAGNETIC THEORY AMD
ELECTRO DYNAMICS
Time: Three hours ' - , Maximum: 100 marks \
SECTION A {20 xl = 20 marks)'
Answer ALL questions.
-Choose the correct answer:
i. Current density is
(a) Rotational (b) Irrotaiional
2. Power radiated by to electric dipole is proportional to the fourth power of the
{jff Frequency (b) Length
(c) Diameter (d) Current.
3. Good conductor of electricity are opaque to
Voltage (b) Current ,
(c) Light . (A) Watt.
4, la polarisation, the positions of the electrons are altered from their equilibrium value while -remain stationary.
(a) Frequency (b) FL.
(c) Wavelength Nuclei.
5, Space time interval is invariant under
-iransfcrmation
Lorentz (b) Gauss
(c) Maxwell (d) Electromagnetic,
8. The t. total bound Asarge on a dielectric is
7. Dimension of poynting vector is fo* (f
I " eff -
x 8. of the #s remains unchanged by
reflection and refraction.
9. Dimension of Thomson Scattering cross section is
10. Tensor equations are tinder co-ordinate transformation.
Match the following :
(a) Classical radius of electron
(b) Four dimensionai
divergence operator v"i''
(c) Sar&cediargedensity 1'
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13. #
14. r0 (d) Scattering angle I'h
f
I
I
. 15. D (e) Radiation resistance.*}
; ' , Answer in 1 or 2 sentences :
I
16,. Define electrostatic energy.
i
'* ' ' 17. Explain End-fire array,
13. Define Snells law,
.......- - ' 19. What is meant by dispersion?
i 20. Explain Lorentz force law.
SECTION B (5 x 6 = 30 marks) Answer ALL questions, choosing either (a) or (b>.
i, 21. (a) - Prove that gradj -
r3;
Or
(b) Use Gausss theorem to obtain the field due to an infinite, straight uniformly charged wire.
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22. (a) Derive an expression for displacemei current.
Or
(b) Starting with, the equation of continuity and assuming Ohm's law, show that the charge density in a conductor obeys the equation:
23. (a) A plane electromagnetic wave travels through a uniform plasma. Calculating the pointing vector, show that it vanishes if the frequency of the wave is equal to the plasma frequency.
Or
Tfl-al is a rave fude? .Discuss the propagation of electromagnetic waves along a hollow wave guide of uniform cross section,
24. (a) Differentiate between Coherence and incoherence in sealtered light. . .
Or
(b) What is meant by Resonance Scattering?
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25. (a)' Derive expression for Lorentz force on a charged particle by Lorentz transformation of force.
Or
(b) Finding the component of wave four vector, show that its square is zero.
SECTION C (5x10 = 50 marks)
Answer ALL questions, choosing either (a) or (b).
26. (a) Deduce Clausius-Mossotti relation and derive Lorenti-Lorentz formula.
Or
(b) Derive and expression for the Magnetic Scalar potential.
27. (a) Starting' from Maxwells equation, * prove
(i) Coulombs law (ii) Continuity equation. '
Or
(b) Derive expressions for electric and magnetic field due to an oscillating dipole.
28, (a) Derive Rayleighs resistance formula for weak skin effect.
Or
(b) What are the peculiarities of metalic reflection? Give its theory in brief and describe a method for its verification.
29, (a) Derive expression for Thomson Scattering Cross-section in terms of classical electromagnetic radius.
Or
Co) Show that the scattering cross section when plane monochromatic waves are incident on
{1} Free electron is af = r02
*5
(ii) Bound electron a =
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30, (a) Write the Lorentz force equation in covariant form and explain the easing of the fourth component of the fou1* density force vector.
(b) Derive the covariant form of the Lorentz force equation mi then show that the three dimensional integration of this equation describes the conservation laws of momentum, and energy,
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