What is emf of electric cell ??

What is EMF ?

Electromotive Force and Internal Resistance

The electromotive force (e) or e.m.f. is the energy provided by a cell or battery per coulomb of charge passing through it, it is measured in volts (V). It is equal to the potential difference across the terminals of the cell when no current is flowing.

electromotive force

  • e = electromotive force in volts, V
  • E = energy in joules, J
  • Q = charge in coulombs, C

Batteries and cells have an  internal resistance (r) which is measures in ohm’s (W).When electricity flows round a circuit the internal resistance of the cell itself resists the flow of current and so thermal (heat) energy is wasted in the cell itself.

electromotive force equation

  • e = electromotive force in volts, V
  • I = current in amperes, A
  • R = resistance of the load in the circuit in ohms, W
  • r = internal resistance of the cell in ohms, W

internal resistance

We can rearrange the above equation;

electromotive force equation 2

and then to

electromotive force equation 3

The battery was a huge success. Not only did it swing the scientific community to his side in the debate with Galvani, it was immediately recognized as a useful device. In 1800 William Nicholson and Anthony Carlisle used the current generated by a battery to decompose water into hydrogen and oxygen. Sir Humphry Davy also studied the same chemical effect. In the 1830s Michael Faraday used a battery in his groundbreaking studies of electromagnetism. Other inventors made improvements on Volta’s original design, and soon it was powering telegraphs and doorbells

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