Electric Field Intensity

According to Coulomb's law, the force on a test charge in free space is given by Eq. 2-1 as

This force is not only a function of the source charge q₁ but also of the test charge q_t. When both sides of Eq. 2-1 are divided by q_t the force per unit test charge is obtained. This quantity is a function of the source charge only and is known as the electric field intensity, expressed by

[2-5]

If the source charge and test charge are in a medium other than free space as for example in a liquid dielectric that has dielectric polarization, the electric field intensity is lower than for free space in the ratio of k_r or relative dielectric constant. Thus

[2-6]

Values of relative dielectric constants for several typical media are shown in Table 2-1.