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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 qt. When both sides of Eq. 2-1 are divided by qt 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


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 kr or relative dielectric constant. Thus


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

Last Update: 2011-01-06