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ELECTROMAGNETIC ENERGY AND FORCES

In this chapter we will consider the storage and transformation of energy in

electromagnetic

Systems.

In the evolution of physical theory, two of the most durable principles have been that

of conservation of charge and that of conservation of energy. Although the latter has in

this century been generalised to the concept of conservation of mass-energy, we are not

in this course concerned with mass-energy transformations, and our view of the principle

will be simply that of conservation of energy.

The principle of conservation of energy, and the fact that electromagnetic fields can

exert forces which can do work, inevitably leads to the idea that energy can be stored in

electromagnetic systems. Pursuing mathematical formulae for the amount of energy stored

leads to the discovery that very generał expressions for that quantity can be developed

in terms of the field variables, rather than in terms of the distribution of sources. A

simple way of looking at this result is that the energy is stored within the field itself.

This viewpoint is very commonly adopted in the study of energy and power flow in

electromagneticsystems.