# ELECTROMAGNETIC FIELDS EMF IMPORTANT QUESTION FOR MAY/JUNE 2012 ANNA UNIVERSITY EXAMINATIONS

Anna University Examination May/June 2012
Important Questions

Common To

EC43:Electromagnetic Fields
EC1253  Electromagnetic Fields
080290021:Electromagnetic Fields
147403:Electromagnetic Fields
10144EC404:Electromagnetic Fields

Note: These are only Important questions , These Question May Or May Not be Asked for University Examination

Unit I

1.Derive the expression for electric Field on the axis  at a point h m of a uniformly charged
circular disc  of radius a m with a charge density of ρs c/m2
2. Find the electric field intensity of a straight uniformly charged wire of length ‘L’m
and having a linear charge density of +ρ C/m at any point at a distance of ‘h’ m
3. State and Prove Gauss’s law. List the limitations of Gauss’s law.
4. Find the magnetic field density at appoint on the axis of a circular loop of a radius b that carries a current I
5 Explain coulomb’s Law .three equal positive charges of 4X 10-9 coulomb each are located at three corners of a square ,side 20cm.determine the electric field intensity at the vacant corner  point of the square.

Unit II

1.Circular disc of radius ‘a’ is uniformly charged with a charge density of s  c/m2.  Find the electric field intensity at a point ‘h’ from the disc along its central axis
2. Derive an expression for magnetic field strength, H, due to a current carrying conductor of finite length placed along the y- axis, at a point P in x-z plane and ‘r’ distant from the origin.
3. Derive the expression for the E at a point P due to an electric dipole.
4. Find the magnetic field intensity at the centre O of a square loop of sides equal to 5M and carrying 10A of current

Unit III

1.Solve the laplace’s equation for the potential field in the hompogenous region between the  two concentric conducting spheres with radius ‘a’ and ‘b’ where b>a V=0 at r = b and V =V0 at r=a .find the capacitance between the two concentric spheres.
2.Determine the inductance of a solenoid of 2500 turns wound uniformly over a length of  0.25m on a cylindrical paper tube , 4 cm in diameter .the medium is air
3. A cylindrical capacitor consists of an inner conductor of radius a and an outer conductor of  radius b. The space between the conductors filled with a dielectric whose permittivity ε, the length of the capacitor is L. Determine the capacitance
4.Derive an expression for the inductance of solenoid
5.Show that the  inductance of the cable L = µl/2π (ln b/a) H.
6.Derive an expression for  the capacitance of  a spherical capacitor with conducting shells of radius a and b.

Unit IV

1.Solve one dimensional  Laplace’s equation to obtain the field inside a  parallel plate capacitor and also find the surface charge density at two plates
2.State and prove Poynting theorem.
3.Derive  Maxwell’s  equation  derived  from  Faraday’s  law  both  in Integral and point forms
4. Three capacitors of 10,25 and 50 microfarads are connected in series and parallel. Find the equivalent capacitance and energy stored in each case ,when the combination is connected across a 500 V supply
5.Derive  modified  form  of  Ampere’s  circuital  law  in  Integral  and differential forms
Unit V

1.Derive the expression for the reflection by a perfect dielectric –normal incidence
2.Obtain the wave equation for a  conducting medium
3.Derive the wave equation starting form Maxwell’s equation for free space For good dielectrics derive the expressions for α, β, ν and η.
4. Find α, β, ν and η. for Ferrite at 10GHz  εr = 9, μr = 4, σ = 10 ms/m