# 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)

Electrostatics

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

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