Anna University Chennai B.E Electronics & Communication Engineering B.E/B.Tech DEGREE EXAMINATION, APRIL/MAY 2008, Electromagnetic Field 2008 Question paper

B.E/B.Tech DEGREE EXAMINATION, APRIL/MAY 2008
Fourth Semester
(Regulation 2004)
Electronics and communication Engineering
EC1253-ELECTROMAGNETIC FIELDS
(Common to B.E (Part-time) Third Semester Regulation 2005)
Time:Three hours Maximum:100 marks
Answer ALL questions

PART A –(10*2=20marks)

1. Find the gradient of scalar system t=x²y+e? at point P(1,5,-2).
2. Define Coulomb's law.
3. A long conductor with current 5A is in coincident with positive 'z' direction. If B = 4i + 4j . Find the force per unit length.
4. A steady current of 'I' flows in a conductor bent in the form of a square loop of side 'a' meters. Find the magnetic field intensity at the centre of the loop.
5. Name the magnetic materials.
6. Derive capacitance of a parallel plate capacitor.
7. Define Poynting vector.
8. Determine the EMF developed about the path r=0.5 z=0 and t=0. If B=0.01 sin 377t.
9. Define Skin effect.
10. State Brewster angle.

PART - B (5*16=80 marks)
11. (a)(i) Explain potential due to charged disc.
(ii) Three charged cylindrical sheets are present in three spaces with
s=5C/m² at R=2m s=-2C/m² at R=4m & s=-3C/m² at R=5m. Find
flux density at R=1,3,4,5 and 6m.
Or
(b)(i) Show that Electric field due to 'n' number of charges
n
E = 1/ 4pe S Qi / | ri | ² a ni
i=1

(ii) Prove Div D = ? using Gauss law.
(iii)Two small diameter 10gm dielectric balls can slide freely on a vertical channel. Each carry a negative charge of 1µC. Find the separation between the balls if the lower ball is restrained from the moving.

12. (a)(i) Derive an expression for Magnetic Gauss law in point form and integral form.
(ii) Explain the magnetic field intensity due to a straight wire.
Or
(b)(i) Find the force exerted between current conductors kept in '1' meter distance and carries the current in the same direction.
(ii) Explain the Magnetic field intensity due to a circular loop.

13. (a)(i) Three point charges 1,2,3 coulombs are situated in free space at the corners of an equilateral triangle of side 1m. Find the energy stored in the system.
(ii) Show that the inductance of the cable L= µl / 2 p ln b/a H.
Or
(b)(i) Explain Magnetic boundary conditions with neat sketches.
(ii) Parallel plate capacitor is of area 1m² and has a separation of 1mm. The space between the plates is filled with dielectric of S n = 25 . If 1000 V is applied, find the force squeezing the plates together.

13. (a)(i) Prove that Modified ampere's law consistent with time varying field.
(ii) Calculate the maximum EMF induced in a coil of 4000 turns of radius of 12cm rotating at 30rps in a magnetic field 500 Gauss.
Or
(b)(i) Show that Energy produced per unit volume per second is equal to sum of energy stored per unit volume per second and the energy crossed per unit volume per second.
(ii) Write the Maxwell's equation in point and integral forms.

15. (a) Briefly explain about the wave incident
(i) Normally on a perfect dielectric.
(ii) Obliquely to the surface of perfect insulator.
Or
(b)(i) Derive the general wave equation.
(ii) Derive the equation for plane waves in
(1) Free space.
(2) Homogeneous material
(3) Conducting medium.