### Anna University–Electromagnetic Theory (EMT)–Nov / Dec 2011 Question Paper

B.E/B.Tech DEGREE EXAMINATION NOVEMBER/DECEMBER 2011
B.E. Electrical and Electronics Engineering
Third Semester
131302 - ELECTROMAGNETIC THEORY
(Regulation 2010)
Time: Three hours
Maximum: 100 marks

PART A -(10X2=20 marks)

1. Given two vectors: P = 3i+5j+2K and Q = 2i-4j+3k Determine the angular separation between them.
2 What is the physical sign1ficaceof curl of a vector field?
3 What is meant by conservative property of an electrostatic field?
4. Give the significant physical differences between Poisson’s and Laplace’s equations.
5. State the conservation of magnetic flux.
6. Define magnetostatic energy density.
7 Find the emf induced in a circuit having an inductance of 700 µH if the current through it varies at the rate of 5000A/sec.
8.Distinguish between conduction and displacement currents.
9.Determine the intrinsic impedance of free space.
10.Define voltage reflection coefficient at the load end of a transmission line.

PART B - (5 x 16= 80 marks)

11. (a) (1) What are the sources and effects of electromagnetic fields ?(4)

(ii) Explain the different coordinate systems used to represent field vectors. (12)

Or

(b) State and prove (i). Divergence theorem and (ii) Stroke's theorem (16)

12. (a) (i) State and explain Coulomb’s law of forces. (6)

(ii) Derive the electrostatic boundary conditions at the interface between two dielectrics (10)

(b) (i) The relative permittivity εr, homogeneous isotropic dielectric material is 3.6 and the material is covering the space between z = O and z = 1. If V= 6000z volts in the material,
Find (1)P  (2) E (3) ρs.

(ii) Determine the capacitance of a capacitor consisting of two parallel metal plates 3Ocm x 30 cm surface area, separated by 5 mm in air. What is the total energy stored by the capacitor if the capacitor is charged to a potential difference of 500V? What is the energy density? (8)

13 (a) (ì) Derive an expression for the magnetic field intensity at a point P in a medium of permeability ‘µ’ due to an infinitely long current carrying conductor at a distance r’ meters from the point (10)
.
(ii)If the vector potential is given by A = i5( x2+y2+z2)-1 Wb/m find the magnetic flux density B. (6)

Or

(b) (i) What is magnetization? Explain the classification of magnetic materials with examples. (10)

(ii) An iron ring with a cross-sectional area of 3cm2 and a mean circumference of 15cm is wound with 250 turns of wire carrying a current of 0.3A. The relative permeability of the ring is 1500.
Calculate the flux established in the ring. (6)

14.(a) State and derive the time-harmonic Maxwell’s equations in integral form and point form. Why are Maxwell’s equations not completely symmetrical ? (16)

(b) By means of a simple RLC series circuit, explain the relationship between the field theory and circuit theory. Also explain the limitations of circuit theory. (16)

15. (a) (i) Derive the electromagnetic wave equations in phasor form. (12)

(ii) The current density at the surface of a thick metal plate is 100 A/m2. What is the skin depth if the current density at a depth of 0.01 cm is 28A/m2? (4)

Or

(b) (i) How is power flow referred by using Poynting Vector? Explain Poynting’s theorem. Explain its significance. (12)

(ii) What is Standing Wave Ratio? Write the relationship between standing wave ratio characteristic impedance and input impedance of a transmission line. (4)