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Assumptions

In our analysis we make a number of assumptions. The first of these is that the length of

the linę runs along a z axis and that the linę characteristics are uniform with respect to the z axis. This second assumption is madę to enable an appropriatly simple analysis. The third assumption is that such magnetic fields as exist are confined to the transverse

piane, that is the piane perpendicular to that z axis. This assumption enables us toconclude that the linę integral of the clectric field from a point on one of the conductors

to anothcr point in the same transversc piane on another conductor is independent of the

path, and therefore one may speak meaningfully of the voltagc betwccn the two conductors

in a piane defincd by a particular value of the z co-ordinate.

The fourth assumption is that the currents which flow in the two conductors are equal in niagnitudc and oppositc in direction.

We also assume that the currents flow uniformly on the surfaces of the conductors rather than being distributed over their cross section. Our reasons for making this assumption

howevercan not be madę elear until Chapter 9, dealing with the behaviour of electromagnetic fields in dissipative media, wherein the effect known as skin effect is introduced.