Introduction of Electromagnetic Fields

By Rahul Singh|Updated : January 17th, 2017

Electromagnetic theory is a discipline concerned with the study of charges at rest and in motion.




  • Electromagnetic theory is a discipline concerned with the study of charges at rest and in motion.
  • Electromagnetic principles are fundamental to the study of electrical engineering and physics.
  • Electromagnetic theory is also indispensable to the understanding, analysis and design of various electrical, electromechanical and electronic systems.
  • Applications:RF communication, Microwave Engineering, Antennas, Electrical Machines, Satellite Communication, Atomic and nuclear research, Radar Technology, Remote sensing, Quantum Electronics, VLSI, etc.
  • Electromagnetic theory can be thought of as generalization of circuit theory.
  • There are certain situations that can be handled exclusively in terms of field theory.
  • In electromagnetic theory, the quantities involved can be categorized as source quantities and field quantities.
  • Source of electromagnetic field is electric charges: either at rest or in motion.
  • However an electromagnetic field may cause a redistribution of charges that in turn change the field and hence the separation of cause and effect is not always visible.
  • Electric charge is a fundamental property of matter.
  • Electromagnetic fields are caused by electric charges at rest and in motion.
  • Positive and negative electric charges are sources of the electric fields and moving electric charges yielding a current is the source of magnetic fields.
  • Charge exist only in positive or negative integral multiple of electronic charge, -e, e = 1.60 × 10-19 coulombs.
  • Time-varying electric and magnetic fields are coupled in an electromagnetic field radiating from the source.
  • Electromagnetic theory deals directly with the electric and magnetic field vectors where as circuit theory deals with the voltages and currents.
  • Voltages and currents are integrated effects of electric and magnetic fields respectively.
Electromagnetic fields are divided into four different quantities:
  • Magnetic flux density (B) with the unit T (Tesla or volt-second per square meter)
  • Magnetic field intensity (H) with the unit A/m (Ampere per meter)
  • Electric field intensity (E) with the unit V/m (Volt per meter)
  • Electric flux density (D) with the unit C/m2 (Coulomb per square meter)


Charge Distribution : In electrostatics we deal with point charges and different types of charge distriubutions like volume charge distribution, line charge distribution and surface charge distribution.
Volume Charge Distribution : 
  • It is defined as charge per unit volume.


where, ΔQ is small amount of charge in small volume ΔV.

  • The total charge within a defined volume is obtained by taking the volume integral throughout the volume.

00-Introduction-of-Electromagnetic-fields (2)

Where, ρv = volume charge density, and dV = Differential volume

Line Charge Distribution: 
  • In line charge distribution, whole the charge is linearly distributed along the length of the line and it is defined by liner charge density.
  • It is the charge per unit length.

00-Introduction-of-Electromagnetic-fields (3)

where, ρL = Linear charge density, and dL = Differential length

Surface (Sheet) Charge Distribution: 
  • In surface charge distribution, the charge is uniformly distributed over the surface of sheet and it is defined by surface charge density.
  • It is charge per unit surface area.

00-Introduction-of-Electromagnetic-fields (4)

Here, ρS = Surface charge density, and dS = Differential area.



write a comment

Follow us for latest updates