EC-504-A Electro Magnetic Theory - Dec 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aState Coulomb's Law in vector form. Define electric field intensity and electric flux density. Derive the relation between D and E.
   How to answer

   • State Coulomb's law in vector form with formula
   • Define electric field intensity E
   • Define electric flux density D
   • Derive relation D = epsilon E
2. 7 Marks
   bExplain Gauss's law and derive the expression for electric field due to an infinite line charge. Two point charges $+6\mu C$ and $-4\mu C$ are separated by $0.3m$. Find the electric field intensity at the midpoint.
   How to answer

   • State Gauss's law in integral and differential form
   • Apply to infinite line charge using cylindrical Gaussian surface
   • Derive E = rho_l / (2 pi epsilon rho)
   • Calculate E at midpoint due to +6uC and -4uC charges
3. 7 Marks
   aExplain divergence and curl of a vector field with physical significance.
   How to answer

   • Define divergence of vector field with formula
   • Define curl of vector field with formula
   • Explain physical significance of divergence as source density
   • Explain physical significance of curl as rotation
4. 7 Marks
   bUsing the method of images, find the electric field due to a point charge near an infinite grounded conducting plane.
   How to answer

   • State method of images principle for grounded plane
   • Replace plane by image charge -Q
   • Calculate potential and field by superposition
   • Show tangential E zero on plane
5. 7 Marks
   aDerive the expression for magnetic field intensity due to a long straight current-carrying conductor.
   How to answer

   • State Biot-Savart law or Ampere's circuital law
   • Apply to long straight conductor with symmetric Amperian loop
   • Integrate to get H = I / (2 pi rho)
   • Give direction by right-hand rule
6. 7 Marks
   bState and explain Stokes theorem. A capacitor has plate area $0.01\, m^2$ and separation $1mm$. If the electric field varies with time, calculate the displacement current.
   How to answer

   • State Stokes theorem relating line and surface integrals
   • Explain with diagram and physical meaning
   • Define displacement current density
   • Calculate displacement current for given capacitor
7. 7 Marks
   aDerive the force per unit length between two parallel current-carrying conductors.
   How to answer

   • Find magnetic field due to one conductor
   • Calculate Lorentz force on second conductor
   • Obtain force per unit length formula
   • State attractive/repulsive condition
8. 7 Marks
   bAssuming that all the energy from a 1000-Watt lamp is radiated uniformly: calculate average values of the intensities of electric and magnetic fields of radiation at a distance $5m$ from the lamp.
   How to answer

   • Calculate average Poynting vector from total power
   • Use S = E_rms x H_rms relation
   • Find E_rms and H_rms at 5m
   • Convert to peak values if required
9. 7 Marks
   aExplain displacement current and derive Maxwell's correction to Ampere's Law.
   How to answer

   • Define conduction vs displacement current
   • Show inconsistency in Ampere's law for time-varying fields
   • Add displacement current term
   • Write Maxwell's correction
10. 7 Marks
    bState and explain Faraday's Law of electromagnetic induction. Derive equation of continuity.
    How to answer

    • State Faraday's law of electromagnetic induction
    • Explain induced emf with Lenz's law
    • Apply charge conservation principle
    • Derive continuity equation div J + d rho_v/dt = 0
11. 7 Marks
    aDerive Maxwell's equations in differential form and explain their significance.
    How to answer

    • Write four Maxwell equations in differential form
    • Derive from Gauss, Faraday and Ampere-Maxwell laws
    • Explain physical significance of each
    • Mention free-space form
12. 7 Marks
    bExplain Poynting vector and Poynting theorem.
    How to answer

    • Define Poynting vector S = E x H
    • Derive power balance equation
    • State Poynting theorem
    • Explain energy flow significance
13. 7 Marks
    aDerive the electromagnetic wave equation in free space.
    How to answer

    • Start from Maxwell's equations in free space
    • Take curl of E and H equations
    • Obtain wave equations for E and H
    • Identify velocity c = 1/sqrt(mu0 epsilon0)
14. 7 Marks
    bDerive reflection coefficient for a plane wave at normal incidence. Explain reflection of a plane wave at oblique incidence.
    How to answer

    • Apply boundary conditions at normal incidence
    • Write incident, reflected and transmitted fields
    • Derive reflection coefficient Gamma
    • Extend discussion to oblique incidence with Snell's law
15. 7 Marks
    aDerive expressions for plane electromagnetic waves in dielectric medium Explain boundary conditions for electric and magnetic fields.
    How to answer

    • Write Maxwell's equations in dielectric medium
    • Derive wave equation and propagation constant
    • State boundary conditions for E, D, B, H
    • Explain tangential and normal components
16. 7 Marks
    bDerive expressions for attenuation constant, phase constant and skin depth in a conducting medium.
    How to answer

    • Start from wave equation in conducting medium
    • Define propagation constant gamma = alpha + j beta
    • Derive alpha and beta expressions
    • Derive skin depth delta = 1/alpha