ELECTROMOTIVE FORCE (EMF)

Current needs a “push” to get its flow started. In a battery, this push is produced by the difference in charge at the two opposing terminals. The electrons’ urge to flow from the negative terminal to the positive terminal will get a current started. Whenever a positive charge and a negative charge are positioned close to each other, electromotive force exists. Electromotive force, often abbreviated EMF, is a force that tends to move electricity.

The term potential is also used to describe EMF. That is, in a battery, the potential or ability to generate current is present. All you have to do is connect wires to the battery to give  the electrons a path to flow on.

          When free electrons are dislodged from atoms, electrical energy is released. Chemical reaction, friction heat and electromagnetic induction will cause electrons to move from one atom to another. Whenever energy in any form  is released, a force called electromotive (e. m. f.) is developed.

         If the force exerts its effort always in one direction, it is called direct; and if the force changes its direction of exertion periodically, it is called alternating. The chemical reaction in a dry cell, heat and friction are sources of a unidirectional force. Electromagnetic induction produces an alternating force. The direction of force depends on the direction in which the field is cut. Whenever an e. m. f. is developed, there is also a field of energy called an electrostatic field, which can be detected by an electroscope and measured by an electrometer.

ELECTROMOTIVE FORCE AND RESISTANCE

      The electromotive force is the very force that moves the electrons from one point in an electric circuit towards another. In case this e. m. f. is direct, the current is direct. On the other hand, were the electromotive force alternating, the current would be alternating, too. The e. m. f. is measurable and it is the volt that is the unit used for measuring it. A current is unable to flow in a circuit consisting of metallic wires alone. A source of an e. m. f. should be provided as well. The source under consideration may be a cell or a battery, a generator, a thermocouple or a photocell, etc.

      In addition to the electromotive force and the potential difference reference should be made to another important factor that greatly influences electrical flow, namely, resistance. All substances offer a certain amount of opposition, that is to say resistance, to the passage of current. This resistance may be high or low depending on the type of circuit and the material employed. Glass and rubber offer a very high resistance and, hence, they are considered as good

insulators. All substances do allow the passage of some current provided the

potential difference is high enough.

      Certain factors can greatly influence the resistance of an electric circuit. They are the size of the wire, its length, and type. In short, the thinner or longer the wire, the greater is the resistance offered.

More links:

Electromotive force

What is Electromotive Force?