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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI 600 034
M.Sc.DEGREE EXAMINATION PHYSICS
FIRSTSEMESTER APRIL 2018
17PPH1MC02/PH 1818- ELECTRODYNAMICS
Date: 02-05-2018 Dept. No. Max. 100 Marks
Time: 01:00-04:00
PART A
Answer ALL questions: (10 x 2 20)
1. Establish Ampere's law in differential and integral form.
2. Show that the electrostatic potential satisfies superposition principle.
3. State Poynting's theorem.
4. What is a gauge transformation? Give an example.
5. Define skin depth.
6. State the Einstein velocity addition rule.
7. Define radiation zone.
8. Give the Larmor formula for power radiated by a point charge.
9. What is cut-off frequency with reference to a waveguide?
10. Find the cut-off frequency for a given wave guide in the TE10 mode.
PART B
Answer any FOUR questions: x 7.5 30)
11. A long cylinder carries a charge density that is proportional to the distance from the axis ks for some constant k. Find the electric field inside the cylinder.
12. Derive expressions for energy and momentum of electromagnetic waves.
13. A pion at rest decays into a muon and a neutrino. Find the energy of the outgoing muon in terms of the two masses, and (assume Also find the velocity of the outgoing muon.
14. An infinite straight wire carries a current 0 (for t and I0 (for t 0). Find the resulting electric and magnetic fields.
15. Consider a rectangular wave guide with dimensions 2.28 cm x 1.01 cm. What TE modes will propagate in this wave guide, if the driving frequency is 1.70 x 1010 Hz?
16. Why TEM mode is not possible in a hollow waveguide? Show that a coaxial transmission line support TEM waves.
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PART C
Answer any FOUR questions: (4x12.5=50)
17. Derive the expression for multipole expansion of vector potential.
18. Derive Fresnel's equation for reflection and transmission at oblique incidence.
19. Give the complete set of transformation equations among the components of electric and magnetic fields. Show that E.B is Lorentz invariant.
20. Obtain Leinard-Wiechert potentials for a moving point charge.
21. What are waveguides? Obtain the general expressions for the longitudinal components Ez and Bz.
22. Derive an expression for the power radiated by an oscillating point charge.