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Electromotive Force

What is Electromotive Force?

Electromotive force is defined as the electric potential produced by either electrochemical cell or by changing the magnetic field. EMF is the commonly used acronym for electromotive force.

A generator or a battery is used for the conversion of energy from one form to another. In these devices, one terminal becomes positively charged while the other becomes negatively charged. Therefore, an electromotive force is a work done on a unit electric charge.

Electromotive force is used in the electromagnetic flowmeter which is an application of  Faraday’s law.

Symbol for Electromotive Force

The electromotive force symbol is ε.

What is Electromotive Force Formula?

Following is the formula for electromotive force:

ε = V + Ir


  • V is the voltage of the cell
  • I is the current across the circuit
  • r is the internal resistance of the cell
  • ε is the electromotive force

What is the unit of EMF?

The unit for electromotive force is Volt.

EMF is numerically expressed as the number of Joules of energy given by the source divided by each Coulomb to enable a unit electric charge to move across the circuit.

\(\begin{array}{l}Volts=\frac{Joules}{Coulombs}\end{array} \)

Dimension of Electromotive Force

EMF is given as the ratio of work done on a unit charge which is represented as follows:

\(\begin{array}{l}EMF=\frac{Joules}{Coulombs}\end{array} \)

Therefore, EMF dimension is given as M1L2T-3I-1

Difference between Electromotive Force and Potential Difference

Electromotive Force  Potential Difference
EMF is defined as the work done on a unit charge Potential difference is defined as the energy which is dissipated as the unit charge pass through the components
EMF remains constant Potential difference is not constant
EMF is independent of circuit resistance The potential difference depends on the resistance between the two points during the measurement
Due to EMF, electric, magnetic, and the gravitational field is caused Due to the potential difference, the only electric field is induced
It is represented by E It is represented by V

Can electromotive force be negative?

Yes, the electromotive force can be negative. Consider an example where an inductor is generating the EMF such that it is opposing the incoming power. Then the produced EMF is taken as negative as the direction of flow is opposite to the real power. Therefore, the electromotive force can be negative.

What is the difference between terminal voltage and EMF?

Following are the difference between terminal voltage and EMF:

  • Terminal voltage is defined as the potential difference across the terminals of a load when the circuit is on. While EMF is defined as the maximum potential difference that is delivered by the battery when there is no flow of current.
  • A voltmeter is used for measuring the terminal voltage whereas a potentiometer is used for measuring the EMF.

Below is the video explaining how an EMF is induced due to the motion of a conductor in a magnetic field:

Test Your Knowledge On Electromotive Force!


  1. Its very helpful for the students

  2. thanks it’s very helpfull

  3. Nice, this explanation is good.

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