Difference Between Electromotive Force (emf) and Potential Difference

Electromotive Force (emf) vs Potential Difference

Electromagnetism is an integral part of physics. There are terms and units which are very closely related to each other and have a very fine line distinguishing the two. “Potential difference” and “emf” are two such terms.

Electromotive Force (emf)

Electromotive force, or emf, is better described as the total voltage in an electric circuit generated by the source or battery. Emf is not a physical force. It is basically the energy required to move a unit positive charge from the negative terminal of the battery to the positive terminal when the circuit is open. Emf is the underlying voltage that occurs by the fluctuating magnetic field across a wire or circuit. Formally, it was also defined as the force which is required to separate two charges (one positive and one negative) from each other.

It is measured in volts. Electromotive force is often denoted by the symbol ‘ℰ’ (epsilon).
Mathematically, if we define emf, we get:
Where ‘ℰ’ is the emf and ECS is the electrostatic field generated.

In simple words, it may be stated as electromotive force is the maximum voltage that can be attained by a specific circuit.

Potential Difference

Potential difference is the work done per unit charge to move a charge between the negative and the positive terminal of the battery. When the battery is in use, or the circuit is closed, a small portion of the emf is spent in overcoming the internal resistance of the battery. This energy per unit charge is called potential difference.

If ‘ℰ’ is the emf of the battery used in the circuit and ‘r’ is the internal resistance of the specific battery and the external resistance of the circuit is ‘R’ in a circuit of ‘I’ current then;
ℰ = Ir + IR
Here, ℰ – Ir is regarded as the potential difference between the terminals of the battery which is also known as the terminal voltage.
The emf can be measured using a voltmeter and is represented by the symbol ‘V’ (volt).
The term “potential difference” is also used in relation to magnetic and gravitational fields. Their units are different but the concept is similar.

Summary:

1.Emf is the total voltage in the battery while the potential difference is the work done in moving a charge against the electric field between two specific points in the circuit.
2.Emf is always greater than the potential difference.
3.The concept of emf is applicable only to an electrical field while the potential difference is applicable to magnetic, gravitational, and electric fields.

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