Voltage and Resistance

Local Mobile Advertising
Local Coupons

The ability of an energy source (e.g. a battery) to produce a current within a conductor may be expressed in terms of electromotive force  (e.m.f.). Whenever an e.m.f. is applied to a circuit  a potential difference  (p.d.) exists. Both e.m.f. and p.d. are measured in volts (V). In many practical circuits there is only one e.m.f. present (the battery or supply) whereas a p.d. will be developed across each component present in the circuit.
The conventional flow of current in a circuit is from the point of more positive potential to the point of greatest negative potential (note that electrons move in the  opposite  direction!). Direct current results from the application of a direct e.m.f. (derived from batteries or a d.c. power supply). An essential characteristic of these supplies is that the applied e.m.f. does not change its polarity (even though its value might be subject to some fluctuation).

For any conductor, the current flowing is directly proportional to the e.m.f. applied. The current flowing will also be dependent on the physical dimensions (length and cross-sectional area) and material of which the conductor is composed.
The amount of current that will flow in a conductor when a given e.m.f. is applied is inversely proportional to its resistance. Resistance, therefore, may be thought of as an opposition to current flow; the higher the resistance the lower the current that will flow (assuming that the applied e.m.f. remains constant).