Difference Between EMF and Voltage (with Table)

The difference between EMF and voltage is in terms of their definitions. The former is a measure of voltage that is produced within an electrical source. It is the energy provided by a cell to per unit coulomb charge that is passing through the cell. Voltage, on the other hand, is the difference in potential energy between two points in a circuit.

EMF is equal to the potential difference between the two poles when no current is flowing through the circuit. Voltage refers to the energy needed to transfer an electric charge from one end of the circuit to another divided by the magnitude of the charge. Thus, although EMF and voltage are intrinsically linked, they are also significantly different.

Comparison Table Between EMF and Voltage

Parameters of ComparisonEMFVoltage
DefinitionDefined as voltage produced within an electrical source.Defined as the potential difference between two given points in a circuit.
FormulaΕ =I (R+r)  V= I + R  
IntensityConstant intensity maintainedIntensity is not constant
Measuring InstrumentMeasured with an EMF meter.Measured with a Voltmeter.
Force operationCoulomb force operation.Non-Coulomb force operation.
SourcesDynamo, electrochemical cells, solar cells.Electric and magnetic fields.

What is EMF?

EMF is short for Electromotive Force which is defined as voltage produced within an electric cell. Energy is converted from one form to another in a generator or battery. For this purpose, one terminal of the generator or battery becomes positively charged and the other becomes negatively charged.

Work done per unit charge is denoted by EMF. EMF is the energy provided by a cell or battery per unit of coulomb of charge passing through it. When no current is flowing through the circuit, EMF is equal to the potential difference between the two terminals. Volt is the unit of measuring EMF. The symbol of EMF is ε.

There are several alternative formulas to calculate EMF.

  1. ε = V + Ir
  2. V is used to connote the voltage of the cell
  3. I is used to connote the current flowing through the circuit
  4. r is used to connote the internal resistance of the cell
  5. and, ε is used to connote EMF

Another formula used to find out EMF is:

  • ε = E/Q where,
  • ε signifies EMF
  • E signifies energy in Joules
  • Q signifies charge in coulomb

The formula can be altered taking into account the internal resistance of the cell. Then we derive another method for calculating EMF:

  • Ε =I (R+r)
  • ε signifies EMF
  • I signifies the current flowing through the circuit
  • R signifies the resistance offered by the circuit
  • R signifies the internal resistance of the cell.

CNX UPhysics 27 03 InternalR

What is Voltage?

Voltage is defined as the amount of potential energy flowing between two points in a circuit. It is also defined as the amount of potential energy available per unit charge.

Voltage can also be defined as the pressure needed to push per unit electrical charge through a conducting loop in a circuit. It is the work done to move a unit charge from one point in the circuit to another.

The unit of measurement for voltage is the same as EMF. Named after the Italian scientist Alessandro Volta, this unit of measurement is shared by both EMF and voltage. Volta was credited to have discovered the first electronic battery.

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Voltage is thus denoted in equations as ‘V’. Voltage is a product of electric and magnetic fields. Ohm’s law is used to calculate the voltage drop for each resistor. The common symbols for voltage include V, ∆V, U, ∆U.

The formula for calculating voltage:

                      V= I + R where,

  • V connotes voltage
  • I connotes the current flowing through the circuit
  • R connotes the resistance

voltage basic illustration 01

Main Differences Between EMF And Voltage

  1. The main difference between EMF and voltage is that the former represents the voltage inside each electrical source, while the latter represents the potential difference between two given points.
  2. The intensity of EMF is constantly maintained. The intensity of voltage charges can fluctuate. Thus, voltage does not have constant intensity.
  3. The third difference between the two can be denoted in terms of the instrument of measurement used for each. EMF is measured using an EMF meter, while voltage is measured with a voltmeter.
  4. Sources of each also offer another point of difference. EMF sources include dynamos, electromagnetic cells, solar cells, etc. voltage is produced by electric and magnetic fields. 
  5. Another notable difference between the EMF and voltage is in terms of force operation. EMF is a Coulomb force operation, while voltage is a Non-Coulomb force operation.
  6. While EMF can be measured between the two terminals when no current is flowing through the cell, voltage can be measured between any given two points. This is a salient difference between EMF and voltage.
  7. Another interesting point of difference is their cause-effect relationship. EMF is the cause of voltage and voltage is the by-product of EMF.

Conclusion

There are several salient differences between EMF and voltage that potently distinguish one concept from another. They differ in terms of their formulas, intensity, measuring devices, force operation as well as sources.

While EMF denotes the measure of the potential difference between the two terminals of a cell when no current is flowing through it. Voltage is the measure of the potential difference between two given points when current is flowing through the cell. The former maintains constant intensity while the latter can fluctuate.

Solar cells, electric generators and electrochemical cells are sources of EMF, while voltage is produced by an electric or magnetic field. Although both these concepts are intimately linked to electrical circuits and current flow, they are significantly different.

References

  1. https://ieeexplore.ieee.org/abstract/document/7275191/
  2. https://ieeexplore.ieee.org/abstract/document/57096/