Module 1 : Electric Field Intensity (Electric Stress)
Lecture 2 : Importance of Electric Field Intensity in the Dielectrics
  • The 'electric field intensity', also known as the' electric field strength', is defined as the electrostatic force F exerted by the field on a unit positive test  charge q, placed at a particular point P in a dielectric. It is denoted by E, and expressed in unit 'Newtons per Coulomb', that is, the force per unit charge.
  • The electric field intensity is measured in its practical units of 'Volts per meter'  (V/m  or  kV/mm).
  • The electric field intensity is often more specifically mentioned as 'electric stress' experienced by a dielectric or an electrical insulating material.
  • The potential difference between two points a and b, having scalar potential in a space charge free electric field *, is defined as the work done by an external source in moving a unit positive charge from b to a,
                                                                                                                                              (2.1)
  • is positive if the work is done in carrying the positive charge from b to a. The maximum magnitude of electric field intensity is therefore, given by the maximum value of the rate of change of potential with distance. It is obtained when the direction of the increment of distance is opposite to the direction of * , in other words, the maximum value of the rate of change of potential is obtained when the direction of * is opposite to the direction in which the potential is increasing most rapidly,
                                                                                                                                                            (2.2)

The operator on by which   is obtained, is thus known as the 'gradient' . The relationship between   and may be written as,
                                                                                                                                                                        (2.3)

  • The electric field intensity is, therefore, numerically equal to the 'potential gradient'.
 
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