Conventional current refers to the convention in which electrical current ( I ) is considered to be a flow of positive charges. The usefulness of this convention is readily observable when dealing with Kirchoff’s Laws ( or Rules ) and the analysis of magnetic fields that encircle a conductor that carries a conventional current. Of course, we now know that electrons have a negative charge, because current actually flows opposite to the original positive designations within a circuit; nonetheless, the relationship between conventional current and the Right-Hand Rule is of such practical importance that it warrants a closer look:
We begin our journey with a diagram of a circuit in which no current is flowing. A normally open ( NO ) switch must be closed in order for current to flow from a region of high ( + ) electrical potential towards one of lower ( – ) electrical potential:
As the circuit is closed, charges flow across the resistor ( R ) to a region where they have less of an ability to perform work. A charge that hypothetically passes through the source from the source’s negative terminal to its positive terminal would experience and increase in electric potential. This increase in electric potential is equally offset by a decrease in electric potential as charges perform work ( with some heat loss ) on the resistor, and thus, the Law of Conservation of Energy is not violated in any way, shape, or form:
Vsource – Vdrop = 0 V
When conventional current flows through a conductor, it is surrounded by a magnetic field ( B ) whose orientation is determined using the Right-Hand Rule. In order to use the Right-Hand Rule, we simply point the thumb on our right hand in the direction of current flow. We then allow our curled fingers to represent the orientation of magnetic flux ( ɸ ) lines that surround the conducting wire at hand:
We are now ready to take a look at the relationship that exists between conventional current, charging capacitor ( C ) plates, electric fields ( E ), and the magnetic fields associated with such a system. The diagram below is that of a capacitor in which charge does not currently flow:
In an electrically static circumstance, an unchanging electric field occupies the space that separates the capacitor plates from one another when the plate is fully charged. An interesting observation is made, however, during the short span of time during which the plates are charging. As it turns out, a changing current gives rise to a changing magnetic field around the conducting wire that is accompanied by a magnetic field with the same orientation immediately surrounding the space between the capacitor plates!!! The removal of charge from one plate causes the charges in the neighboring plate to increase, and it is as if the electric field acts as a substitute for positive charge crossing the gap between capacitor plates:
Under these circumstances, if we point the thumb of our right hand in the direction of the current or E-field, we can accurately predict the orientation of the B-field that emerges when a changing current gives rise to changing polarity across an associated capacitor plate.
RENAISSANCE PHYSICS 