E.m.f Vs. Voltage – The Difference Between Electromotive Force And Voltage Of A Circuit

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Most of us think Electromotive force (EMF) and Voltage is the same thing as their units are alike. Both of these are interrelated but different from each other. Voltage or potential difference is the result of EMF.

However, most people cannot differentiate between these two terms. EMF and Voltage complement each other.


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Voltage

The potential difference between any two points in a circuit is the voltage of those points. It’s the measurement of the required work to move a unit of charge from one point to another. When electric charges move from one point to another, a voltage drop occurs between those two points. This phenomenon results in a voltage or potential difference.

Based on the magnitude of the external resistance, any two points’ voltage can differ from another two points’ voltage. The unit that we use to measure voltage is Volt (V).

In other words, voltage is the measurement of the work done by the charges. So, an electronic appliance’s voltage gives us a hint about how much work we can make it do.

EMF (Electromotive Force)

EMF is the energy required for the movement of charges in an open circuit. The source, i.e., a battery or a moving magnetic field produces EMF. The unit for EMF is the same as for voltage.

The Electromotive force of a circuit is a constant value when the electric circuit has no load connected. If we add a load to a circuit, a decrease occurs in the circuit’s internal resistance. Because EMF depends on the internal resistance, we then get a changed EMF value. Hence, we measure EMF in no-load conditions.

EMF vs. Voltage

Electromotive force and voltage have many dissimilarities according to their functions. Let’s take a look at them.

  1. EMF is the work that the source does on a unit of charge, and voltage is the work that the electric charges do.
  2. EMF is the cause that makes two points have a voltage or potential difference. So, Electromotive force is the cause and voltage is the result.
  3. You can measure electromotive force only at the two endpoints of a circuit but can measure voltages at any two points.
  4. The Electromotive force of an open circuit is a constant value whereas the value of voltage changes if we change the reference points or external resistor’s values.
  5. EMF is only available in an open circuit, and you’ll find a potential difference or voltage in a closed electric circuit.
  6. Electromotive force doesn’t depend on the external resistance of a circuit. However, voltage changes following a proportional relationship with the external resistance.
  7. You’ll get the constant EMF value when there’s no load in the circuit. So, you cannot measure electromotive force when an electric circuit contains a load resistance, but you can always measure the voltages in that situation.
  8. The formula for EMF is E=I (R + r). Here E denotes the electromotive force. “I” is the current passing through the circuit, R is the external resistance, and r is the internal resistance. The formula for Voltage is V=IR. That means, E=V + Ir.
  9. The symbol for EMF is E, and for voltage, it is V.
  10. The 8th point indicates that EMF is always higher than the total voltage. If the circuit doesn’t have any internal resistance, EMF can be of the same value as the overall voltage.
  11. Electromotive force is the sum of all the voltage drops in a circuit, and voltage is the value of voltage drop between any two points.
  12. EMF causes current to pass throughout the whole circuit whereas the voltage does that for every two points.

So, these were the fundamental differences between EMF and Voltage. These two are of similar value when the circuit is open meaning that no current passes through the circuit. As current starts moving in the circuit, the voltage at different points starts changing.

EMF and voltage are correlative terms. So, it’s easy to get confused. I hope now you can differentiate between them after reading the dissimilarities that I stated here.


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