This chapter includes a few basic concepts which are necessary to understand the material in the proceeding chapters, e.g. system of units, magnetic field, Ampere’s law, and laws of electromagnetic induction. The details of systems of units are given in Table 1.
1.2 System of Units
We know from the Coulombs law that electrostatic force “f” between two point charges q1 and q2 placed at a distance “r” given by
Where ℰa is a constant of proportionality and is called absolute permittivity of the medium. For air absolute permittivity is represented by Єo and the ratio Єa/Єo = K is called relative permittivity which is also called the dielectric constant of the medium. It was shown by Maxwell that in general
Where ‘C’ is the velocity of light (3x 1010 Cm/Sec or 3x108 m/Sec). The values of these constants depends upon system of units chosen
Assuming these quantities to be unity, we get
With the assumption it is possible to define unit electric charge and unit Magnetic pole.
In CGS system of units, the unit of force is dyne
So the unit electrical quantity has such magnitude that two such units, concentrated at points 1 cm apart in air will react with a force of 1 dyne and a unit magnetic pole has such magnitude that two such units, concentrated at points 1 cm apart in air, will react with a force of 1 dyne. Later on this unit electrical quantity was given the name stat coulomb, stat ampere, statvolt and stat ohm.
Electromagnetic units were defined and their name was ampere, volt etc. But it was shown latter on that these units are either too large or too small, so practical units were defined e.g. ampere, Henry, volt and ohm.
Now due to difficulties involved in these system MKS system was defined in which unit of force is 1 Newton = 105 dyne. The basic change was