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4.1.1 Electric Dipole
An electric dipole comprises of two equal and opposite point charges that are separated by a distance δ. The resulting dipole moment, μ is expressed as
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(4.1) |
| Figure 4.1 Schematic of a dipole |
Dipole moment is a vector and + μ points from –ve to +ve charge. It has units of C.m.
Total dipole moment per unit volume is defined as Polarization, P i.e.
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(4.2) |
Units of P are C.m-2 i.e. charge per unit area.
In the most simplistic way when all the dipole are aligned in one direction, P can be written as N.m where N is the number of dipole per unit volume.
You should note that P=0 does not mean that the material does not necessarily have dipole moments rather it is likely that vector summation of all the dipole moment is equal to 0, which is always the case if dipoles were, vectorially speaking, randomly distributed.
In the subsequent sections, we will replace displacement 'δ' by 'd' to avoid duplication by other symbols.
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