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Difference Between Voltage and EMF?

Fundamental Difference Between EMF and Voltage?

What is a Voltage?

The required amount of energy to move the unit charge from one point to another is known as Voltage. In other words, voltage is defined as the difference between electric potentials. It is represented by the symbol of capital “V” and measured in Volts denoted by “V” and measured by a voltmeter.

  • One volt is the difference of electric positional equal to one ampere of current dissipates one watt of power between two conducting points.

Or

  • Volt is the potential difference which moves one joule of energy per coulomb charge between two points.

V = J/C = W/A … in Volts

Where:

  • V = Voltage in Volts
  • J = Energy in Joules
  • C = Charge in Columbus
  • W = Work done in joules
  • A = Current in Ampere

Difference Between Voltage and EMF

What is EMF?

EMF or Electromotive Force is the energy supply to the charge by a battery cell. In other words, EMF produces and maintains voltage inside an active cell and supplies energy in joules to each unit of coulomb charge. It is represented by “ε” and the measuring unit is same as voltage i.e. Volt.

EMF is the maximum potential difference between two points of the battery when no current is flowing from the source in case of open circuit. In short, EMF is the cause and Voltage or potential difference is the effect.

E or ε = W/Q … in Volts

Where:

  • E or ε = Electromotive force energy in Volts
  • W = Work done in Joules
  • Q = Charge in Columbus

Related Post: Difference Between Real Ground and Virtual Ground

Comparison Chart Between Voltage and EMF.

CharacteristicsVoltageEMF
Represented SymbolVE or ε
DefinitionVoltage is the potential difference between two points which causes current to flow. It is the amount of energy per unit charge while moving between two points.EMF or electromotive force is the amount of energy supply to the charge by battery cell. It produces voltage inside active battery sources and supplies energy in joules to each coulomb of charge.
ExpressionPotential difference or Voltage causes current to flow between two points.EMF maintains potential difference between two electrodes.
FormulasV = IR

Where

V = Voltage in Volts

I = Current in Amperes

R = Resistance in Ohms

E = I(R + r)

E = W/Q

Where:

E or ε = EMF in Volts

W = Work done energy in Joules

Q = Charge in Coulombs

r = Internal resistance of the battery cell in ohms

Work PerformedWork performed in moving a charge from one point to another through a conductor wire.In a source, external forces work performed in moving a charge from one point to another.
SourcesElectric field and magnetic field.Active devices such as batteries  cell, solar cell, transformer, electrical generators and dynamo, photo diodes etc.
IntensityThe intensity of voltage is lower than EMF and non-constant.EMF has constant intensity with higher magnitude.
ResistanceVoltage depends on the circuit resistance.EMF doesn’t depends on the circuit resistance.
Force OperationVoltage is a Non-Coulomb force operation.EMF is a Coulomb force operation.
Cause/EffectVoltage is the effect of EMF.EMF is the cause of Voltage.
MeasurementVoltage can be measured between any two points. It can be measured by Voltmeter.EMF can be measured between the end terminals when there is no current flowing through it. It can be measured by EMF meter.

Main Differences between EMF and Voltage

Following are the key differences between voltage and EMF

  • The name EMF at first sight implies that it is a force that causes current to flow. But this is not correct because it is not a force but energy supplied to charge by some active device such as a battery.
  • EMF maintains Potential Difference (P.D or Voltage) while Potential Difference causes current to flow.
  • When we say that EMF of a device (e.g. a cell) is 2V, it means that the device supplies energy of 2 joules to each coulomb of charge. When we say that a Potential Difference between point A and B of a circuit (suppose point A is at higher potential) is 2V, it means that each coulomb of charge will give up an energy of 2 joules on moving from point A to B.

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6 Comments

  1. Thank you for your clear and accurate explanation!

  2. Prakash Satpute says:

    what is back emf?

  3. Rajinder Kumar says:

    says:
    i think E.M.F is the voltage of cell when no load is connected , but P.D is the term applied when the cell is connected to the load.

  4. Yagyaraj Sah says:

    says:
    what is the differences between E.M.F.and P.D.F.?

  5. Hemanth Kumar says:

    Voltage , potential difference and emf these three units are same
    Why these units are same?

    1. Oyeleye Damilare says:

      says:
      @ Hemanth Kumar
      potential difference is same as voltage/voltage drop,as the case may be…..

      E.M.F is gotten when supply is not connected to load (i.e in an open circuit) while ;
      Potential Difference/Voltage drop is gotten when supply is connected to load (i.e in a closed circuit)

      i hope this helps.

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