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Electromotive Force (EMF) Vs. Potential Difference

Voltage Another term which is often used interchangeably with emf and potential difference is voltage. However there is a difference between voltage and emf. Voltage is the measure of emf or potential difference, the unit of emf or potential difference is volt.

Electromotive force (EMF) Vs. Potential Difference

Electromotive force (EMF)

The electromotive force is abbreviated as emf. The name is very descriptive since it literally means a force which moves electrons. The emf is the force or pressure which sets electrons in motion. This force is a result of Coulomb's law. According to Coulomb's law the like charges repel while unlike charges attract. The battery by chemical action produces a negative charge at one terminal and a positive charge at the other. The negative charge is simply an excess of electrons while the positive charge is an excess of positive ions. If a closed circuit is connected across the battery a path for electron flow exists between the battery terminals. Free electrons are repelled by the charge on the negative terminal and are attracted by the charge on the positive terminal.

The two opposite charges exert pressure which forces the electrons to flow. Thus, the force or pressure is the result of the attraction of the unlike charges. To summarize, emf is the force which sets the electrons in motion in a closed circuit.

Potential Difference

Another name for the force mentioned above is the potential difference. This name is very descriptive which describes the characteristics of emf in the open circuit.

EMF is the force which causes the electrons to move as discussed previously. However consider the situation shown in the following diagram where the electrons cannot flow because the switch is open.

Nevertheless the battery still produces the same pressure or force as before. Thus the potential for producing the current flow exists even though no current is presently flowing.

As mentioned here potential means the possibility of doing work. If the switch is closed, current flows, the lamp lights and useful work is done.

Therefore whether a battery is connected into a circuit or not it has the potential for doing work. For e.g. it can move another charge either by attraction or repulsion. Even a single electron can repel another electron. If one electron moves as a result of the other electron some small amount of work is done.

In the battery we are concerned with two types of charges rather than a single charge. The electrons at the negative terminal are straining to rush to the positive terminal and cancel out the positive charges there. In the same way the positive ions at the other terminal are straining to draw the electrons. This force is the potential difference. It is the potential for doing work that exists between two Charges.

Voltage

Another term which is often used interchangeably with emf and potential difference is voltage. However there is a difference between voltage and emf. Voltage is the measure of emf or potential difference, the unit of emf or potential difference is volt.

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