Difference Between EMF and Voltage

The primary difference between EMF and voltage is that EMF denotes the voltage present at the terminals of a source in the absence of current flow. In contrast, voltage refers to the voltage at the source’s end when current circulates through the circuit.

What is EMF?

EMF, or electromotive force, occurs when electrons are separated from atoms by consuming energy in the form of chemical, mechanical, or light. This results in electrically charged particles being formed. EMF can be generated by an electrochemical cell or by changing the magnetic field. The unit of measurement for EMF is volts, and the symbol E denotes it.

The voltage at the ends of the power source when a power source does not supply the current to load equals the EMF, as shown in the below circuit.


Formula for EMF


What is Voltage?

Voltage refers to the variation in electrical states on the poles. Electrons move from the negative to the closed electrical circuit’s positive end. Electrical voltage is the amount of work the electric force does in moving the charge from one point to another within the field. The S.I. unit of voltage is volt, which is denoted by V.

The voltage at the ends of the power source when the power source supplies the current to load equals the voltage, as shown in the below circuit.


Formula for Voltage


The formula for voltage can be expressed in terms of work done and charge.


Difference Between EMF and Voltage

1.EMF is the voltage developed between the terminals of a voltage source when the source is not supplying current to the load.It is the potential difference between two points in an electric circuit.
2.The potential difference between the two terminals of the power source when it is not supplying power is open-circuited, and open-circuited voltage is EMF.When the power source is a closed circuit, the potential difference across the source (terminal voltage) is voltage.
3.External forces move a charge between poles in a source.It is the process of transferring electric charge through a wire from one pole to another.
4.EMF formula is E=V+ IrVoltage formula is V=IR
5.EMF is always greater than the voltage. E>VVoltage is less than voltage. V<E
6.A potentiometer can measure EMF.The Voltage dimensional formula is ML2T-3I-1.
7.The SI unit of EMF is volt(V).The SI unit of voltage is volt(V).
8.Non-Columb force or non-electric force defines EMF.Columb force or electric force defines voltage.
9.EMF is induced in electric fields, magnetic fields, and gravitational fields.Voltage is induced only in electric fields.
10.EMF dimensional formula is M1L2T-3I-1The Voltage dimensional formula is ML2T-3I-1

Sample Problems

Problem 1: A circuit has a 4,2 V potential differential and a current of 0.6 A. The internal resistance of the battery is 0.3 ohms. Find EMF.

Given Data-
I= 0.6 A
r=0.3 Ohms



Problem 2: The battery has a terminal voltage of 4 volts and an internal resistance of 0.01 ohms. Calculate the amount of current that is being supplied to a load with a resistance of 1 ohm.

Given Data-
V= 4 Volts
r=0.01 Ohms
R= 1 Ohm




In conclusion, understanding the difference between EMF and voltage is crucial for anyone to comprehend electrical systems and circuits. While both terms are often used interchangeably, they represent distinct concepts in the electrical circuit.

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