### Electromagnetic Theory - Introduction and Definitions

Electromagnetic Theory - INTRODUCTION
Electromagnetic theory is a discipline concerned with the study of charges at rest and in motion.
Both the Positive and Negative Charges are the source of an electric field.
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. Some of the branches of study where electromagnetic principles find application are:

• RF communication
• Microwave Engineering
• Antennas
• Electrical Machines
• Satellite Communication
• Atomic and nuclear research
• Remote sensing
• EMI EMC
• Quantum Electronics
• VLSI

Electromagnetic theory is a prerequisite for a wide spectrum of studies in the field of Electrical Sciences and Physics. 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.

Sources of EMF:
• Current carrying conductors.
• Mobile phones.
• Microwave oven.
• Computer and Television screen.
• High voltage Power lines.

Effects of Electromagnetic fields:
·         Plants and Animals.
·         Humans.
·         Electrical components.

Fields are classified as
• Scalar field
• Vector field.
Electric charge is a fundamental property of matter. Charge exist only in positive or negative integral multiple of electronic charge, -e, e= 1.60 × 10-19 coulombs. [It may be noted here that in 1962, Murray Gell-Mann hypothesized Quarks as the basic building blocks of matters. Quarks were predicted to carry a fraction of electronic charge and the existence of Quarks have been experimentally verified.]

Principle of conservation of charge states that the total charge (algebraic sum of positive and negative charges) of an isolated system remains unchanged, though the charges may redistribute under the influence of electric field.

Kirchhoff's Current Law (KCL) is an assertion of the conservative property of charges under the implicit assumption that there is no accumulation of charge at the junction.

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 field problems involve three space variables along with the time variable and hence the solution tends to become correspondingly complex.
Circuit theory treats resistors,capacitors and inductors as two terminal devices connected by the wires while Field theory deals with the space both inside and outside these devices, providing a three dimensional, real world understanding of how they work.