POTENTIAL DIFFERENCE

When two positive charges or two negative charges are brought near to each other they repel while a positive and negative charge are attracted to each other. Then a charged particle has the ability to do work. The ability of a charged particle to do work is called an electric potential. Thus two dissimilar charges have a difference of potential and the unit of potential difference (p_d) is called the volt. The volt unit of potential difference, named after Alessandro Volta (1745–1827), involves work which is the measure of the amount of work required to move an electric charge, which in turn involves force and distance. The SI unit of work is the joule with unit symbol J, the SI unit of force is the newton with unit symbol N, and the SI unit for distance is the meter with unit symbol m.

W (joules) = N (newtons) x m (meters)

Energy is the capacity to do work. Potential energy, which is the energy a body has because of its physical position.

In electronics, potential difference is commonly referred to as voltage, with the symbol V. Sometimes the symbol U or E for emf (electromotive force) is used, but the standard symbol V represents any potential difference. This applies either to the voltage generated by a source such as a battery or solar cell, or to the voltage dropped across a passive component such as a resistor. The voltage difference (also called potential difference) between two points is the work in joules required to move one coulomb of charge from one point to the other. The SI unit of voltage is the volt and is given as:

A constant voltage is called a DC voltage and a voltage that varies sinusoidally with time is called an AC voltage. A voltage source such as a battery or solar cell provides a constant DC voltage, for example 12 VDC. A voltage source such as an alternator or generator provides an alternating AC voltage, so for example 240 VAC.

If point a is positive with respect to point b, moving a positive charge around a closed circuit from a to b (or a negative charge from b to a) requires work. The difference between the two points is the voltage polarity. This voltage polarity is indicated by a positive sign ( + ) at point a and a negative sign ( - ) at point b.

In the circuit the arrow indicates the direction of current flow. If the arrow points in the same direction of the positive charge carriers (conventional current flow) the numeric vale of the current receives a positive sign, +2A. If current flow is opposite (electron flow), the numerical value receives a minus sign, -2A. The sign indicates the direction of current flow with the arrow ( + ) or in reverse ( - ).

Then Conventional Current Flow gives the flow of electrical current from positive to negative and Electron Current Flow around a circuit from the negative terminal to the positive. The item which provides a path for the electrons to flow is called a conductor.

The polarity of the voltage is also indicated by the direction of an arrow. If the arrow points from more positive to more negative potential, the numerical value of the voltage has a positive sign, +6V. If it points from a more negative to a more positive potential, then the numerical value receives a minus sign, -6V.

The battery symbol is often used to denote a DC voltage source, but it may not always be a battery. Usually the positive ( + ) and negative ( - ) signs are not shown because, by convention, the long end line denotes the positive terminal (the Anode) and the short end line the negative terminal (the Cathode). Thus, it is not necessary to put + and - signs on the diagram