Introduction

Introduction

AU : Dec.-18

• The Maxwell's equations for time varying fields form the basics for the explanation of the electromagnetic wave propagation. The existance of the electromagnetic waves was first stated by Prof. Heinrich Hertz. Actually Prof. Maxwell himself predicted the existance of the electromagnetic (EM) waves earlier. But Prof. Hertz was the first scientist who generated and detected the radio waves successfully. So some time, EM waves are also commonly called Hertzian waves.

• The waves are the means of transporting energy or information from source to destination. The waves consisting electric and magnetic fields are called electromagnetic waves. The electromagnetic waves are said to be in exsistance if all the four Maxwell's equations are satisfied at the source point (where they are generated), at any point in the medium (through which they travel) and at the destination or load point (where they are received). Basically the waves radiated from the source are with spherical wavefront; but at large distances from source the spherical waves become practically plane waves.

• In general, the wave is a function of time and space. The typical examples of the electromagnetic waves are radio waves, light rays, radar beams, television signals etc. All different forms of electromagnetic energy show following important properties :

1. They assume properties of waves while travelling.

2. They travel with high velocity.

3. They radiate outwards from source in all directions.

• The electromagnetic waves travel from source into the surrounding media. The media can be divided into broad category as

i) Lossless media and ii) Lossy media

• The lossless media can be further classified as

 i) Perfect dielectric

ii) Free space

• Similarly the lossy media can be further classified as

i) Good dielectric, ii) Good conductor iii) Perfect conductor

• The properties of any single continuous medium can be explained as follows :

σ = Conductivity of medium

ε = Permittivity of medium = ε₀ε_r

where ε_r = Relative permittivity

ε₀ = Permitivity of free space

= 8.854 × 10^-12 F/m

µ = Permeability of medium = µ₀ µ_r

where µ_r = Relative permeability

µ₀ = Permeability of free space

= 4 π × 10^-7 H/m

Thus in general the classification of a single continuous medium alongwith properties is as shown in the Fig. 10.1.1.

Review Questions

1. What is meant by a wave ? List properties of wave. AU : Dec.-18, Marks 12

2. List different types of media and brief out about them.