APR/MAY 2003 131302 ELECTROMAGNETIC THEORY Third Semester question paper

Third Semester
Electrical and Electronics Engineering
Time : Three hours Maximum : 100 marks
Answer ALL questions.
PART A — (10 ? 2 = 20 marks)
1. Under what conditions will the field intensity be solenoidal and irrotational?
2. State Gauss's law. Under what condition is Gauss's law especially useful in
determining the E–field intensity of a charge distribution?
3. A fixed voltage is applied across a parallel plate capacitor. Does electric flux
density depend on the ? of the medium? Explain.
4. Can a static magnetic field exist in a good conductor? Explain.
5. Compare the usefulness of Ampere's circuital law and Biot–Savart law in
determining B
of a current carrying circuit.
6. Explain the significance of displacement current and eddy current.
7. Why is the H–field immediately outside of a perfect conductor tangential to the
conductor surface?
8. Define Poynting vector. What is the SI unit for this vector?
9. What are the boundary conditions of electro magnetic wave at the interface
between two loss less dielectric media?
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10. Explain the method of images to find field at a point due to a point charge.
PART B — (5 ? 16 = 80 marks)
11. (i) Define Lenz's law with mathematical expression. (4)
(ii) Find the magnetic field intensity at a distance x above an infinite
straight wire carrying a steady current I. (12)
12. (a) Find the potential of a uniformly charged spherical shell of radius R at
points inside and outside. (16)
(b) (i) Given the potential 2
10 sin cos
? ?
? find the electric flux density
D at , 0)
. (10)
(ii) Calculate the work done in moving a 10 ? C charge from point
A (1, 30?, 120?) to B (4, 90?, 60?). Use spherical (r, ? , ? ) co–ordinate
system. (6)
13. (a) Two electrodes at potentials 0 V ? V and V ? 0 volt are separated by a
distance d along z–axis. The region between the electrodes contains a
uniform charge density 0 ? , which is generated by electrode at 0 V and
collected at electrode at 0 V. Calculate the electric field at any point Z.
What is the direction of the field? (16)
(b) Derive Maxwell's curl equations from Ampere's law and Faraday's law.
Express the equations in phasor form for time harmonic fields. (16)
14. (a) Explain the Finite Difference Method to find potential at a point in a
charge free medium. (16)
(b) Two infinite parallel plates separated by a distance d are perpendicular
to x–axis. The plate at x ? 0 is at potential 0 V and that at x ? d is at
potential 0 V ? V . Find the E–field and potential variation between the
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plates by separation of variable method. Plot these parameters versus x.
15. (a) Give a mathematical representation of plane waves propagating in +Z
direction in an infinite loss less dielectric medium. Explain how this
medium is characterised by propagation constant and wave impedance.
(b) A linearly polarised plane wave E ? 10 e? j k, r ?mV m? propagates through
free space at an angle ? with respect to Z–axis. Calculate the average
power flow through 1 m2 surface of circular shape lying on
xy plane with center at the origin. Under what condition power flow will
be maximum? (16)
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