# Electromagnetic Fields EC2253 MJ2014 4th Semester Question Paper

Anna University Question Paper
B.E./B.Tech. DEGREE EXAMINATION, May /June 2014.
Electronics and Communication Engineering
2 nd year
4th Semester
EC2253-Electromagnetic Fields

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Part A

1. In XY plane Q1=100100𝜇𝐶 at (2,3)m,experiences a repulsive force of 7.5N
because of Q2 at(10.6).Find Q2.
3. If the magnetic field B=25𝑥𝑖 + 12𝑦𝑗 + 𝛼𝑧𝑘 (T),find α.
4. Write Biot Savart law.
5. An infinite solenoid (n turns per unit length current I)is filled with a linear material
of susceptibility Xm.Find the magnetic field inside the solenoid.
6. Write the boundry conditions for electric field.
7. Find the pointing vector on the surface of a long straight conducting wire (of
radius b and conductivity)that carries a dirct current I.
8. Stae the flux rule for a nonrectangular loop moving through a nonuniform
magnetic field.
9. A sinusoidal electric intensity of amplitude 250 N/M and frequency 1GHz exists
in lossey dielectric medium that has a relative permittivity of 2.5 and loss tangent
of 0.001.Find the effective conductivity of the lossy medium.
10. What is Skin depth.

Part B

11 a)1] State and Explain the fundamental theorem of divergence and curl.(8)
2]Find the electric field at distance ‘z’ above the center of a flat circular disc of radius
R,Which carries a uniform surface charge σ. (8)
Or
b) 1]Get the relationship between potential and electric field .A dipole consists of two
equal and opposite charges separated by distance d.Find the approximate potential at
points far from the dipole.(6)
2] Find the electric field at distance ‘z’ above the center of a circular loop of radius
r,which carries a uniform line of charge λ(5)
3]Given below the electric field variation find the odd one out (5)
1)E=c(xyi+2yzj+3xzk)
2)E=c(𝑦2𝑖 + 2𝑥𝑦 + 𝑧2𝑗 + 2𝑦𝑥𝑘

12 )a)1)Find the magnetic field at the centre of a square loop which carries a steady
current I,Let R be the distance from the centre to side.Find the field at the center of
a n-sided polygon,carrying a steady current I.Again let R be the center to any side
.Find the formula in the limit ntends to infinity.(8)
2)Find the magnetic field a distance h above the center of a circular loop of radius
R,which carries a steady current I.(8)
Or
b) 1) Derive the Ampere circuital law.(8)
2) Derive the expressions with mutually relate current density J,Magnetic field
B,Magnetic vector potential A.(8)

13) a)1]Derive the expression for the nergy of a point charge distribution .Three point
charges -1nC,4nC,3nC are located at (0,0,0),(0,0,1),(1,0,0) respectively.Find the energy
in the system.(8)
2]A small loop of wire (radis a)lies a distance z above the centre of a large loop (radius b)
The planes of the two loops are parallel and perpendicular to the common axis.Suppose
current I flows in the big loop Find the flux through the little loop.Find the mutual
inductance.(8)
Or
b).1]Write the poission’s and laplace equations(4)
2]Discuss the magnetic boundry conditions (6)
3]Two concentric metal spherical shells of radii a and b are separated by weakly
conducting material of conductivity σ If ther arwe maintained at a potential difference V
What current flows from one to another What is the resistance between the shells?Find
the resistance if b>>a(6)

14) a)1]Explain Ampere’s Circuit law. (8)
2]Derive poynting theorem .(8)
Or
b)1]Desribe the Maxwell’s equations in differential and integral forms.(8)
experiments(8)

15)a)1]Derive the wave equations for electric and magnetic fields (8)
2].The electric field intensity of a linearly polarized uniform plane wave propagating in
the +z direction in sea water is E=100cos(107𝜋𝑡)𝑖 V/mat z=0.the constitutive parameters
of sea water are £r=72,μr=1,and conductivity σ=4 S/m. Determine the attenuation
constant,phase constant,intrinsic impedance,phase velocity,wavelength,skin depth.Also
find the distance at which the amplitude of E is 1% of its value at z=0. (8)
Or
b) 1]Analyse the wave behavior at boundaries under oblique incidence and derive the
Brewster angle.(12)
2]Prove that a linearly polarized wave can be resolved into a right hand circularly
polarized wave and a left hand circularly polarized waves are equal amplitude.(4)