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Electromotive Force and Internal Resistance
Comparing E.M.F. and otential Difference
| Electromotive Force | Potential Difference |
Similarities:
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| Definition The electromotive force (e.m.f.) is defined as the energy per unit charge that is converted from chemical, mechanical, or other forms of energy into electrical energy in a battery or dynamo. |
Definition The potential difference (p.d.) between two points is defined as the energy converted from electrical to other forms when one coulomb of positive charge passes between the two points. |
| Symbol: Denote by the symbol, E. |
Symbol: Denote by the symbol, V |
Terminal Potential Difference
- Terminal potential difference or terminal voltage is the potential difference across the two terminal (the positive terminal and the negative terminal) of an electric source (cell or generator).
- If the internal resistance of the cell is ignored, the terminal potential difference is equal to the e.m.f.
Finding E.M.F and Internal Resistance - The Open Circuit Method
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In open circuit ( when the switch is off), the voltmeter shows the reading of the e.m.f. |
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In close circuit ( when the switch is on), the voltmeter shows the reading of the potential difference across the cell. |
With the presence of internal resistance, the potential difference across the cell is always less than the e.m.f.
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