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do not apply.

Similar considerations apply at a Circuit node - if the node is at a changing potential,

the changing electric flux associated with that potential must be supported by a changing

surface charge density, and if the node has a non-zero physical surface area, there is achanging charge thereon, and the algebraic sum of the currents entering that node is no

longer exactly zero. In relation to Figurę 1.8 this effect will guarantee that the sum of

the currents ii, 12 and i3 is not zero. For steady currents, however, these

considerations

do not apply.

The two effects discussed above lead to elear contradictions of Kirchhoff's current law.

As seen above in the discussion of Kirchhoff s voltage law, an assumption commonly

madę is that the magnetic fields of inductors are confined to just the region of the inductor

as illustrated by the dotted linę in Figurę 1.8. Another assumption commonly madę is that

the electric fields associated with capacitors are confined to a limited region containing

the capacitor as shown by the dotted linę in Figurę 1.8. Such an assumption underlies an

assumption normally madę in lumped Circuit theory, that is that the charge on one piąte

of a capacitor is equal and opposite to the charge on the other.

This situation can be closely approximated in the normal construction of a capacitor

where the plates are close together and have an extensive area and the electric field is

confined largely to the region between those plates. But if the capacitor does not have

this construction, and is opened out so that the plates have significant separation, the

electric field which originates on one piąte might terminate on parts of the Circuit other

than the other piąte, and the assumption of equal and opposite charges on the two plates