القوة الدافعة الكهربية Electromotive force
- Electromotive force (e.m.f.) as the source of energy in driving a unit charge around a complete circuit.
- The energy source converts non-electrical energy to electrical energy.
- Potential difference is a measure of the energy dissipated by a component per unit charge.
- The relationship between total e.m.f. and total potential difference is a consequence of the conservation of energy
E.m.f. as a source of energy
1. The energy source that maintains a constant current in a closed circuit is called a source of electromotive force.
The battery of a circuit is the source of emf for the charges and it increases the electrical energy of the charges passing through it. Energy supplied to the charges are derived from chemical potential energy in the battery itself.
We can think of the source as a "pump" that forces electrons to move through the circuit from the negative terminal of the battery to the positive terminal of the battery.
2. The emf source provides the energy that drives the current round the circuit. Energy gained by the charges as they pass through the battery is lost to in the components
such as resistors and lamps. Hence the battery must continuously convert chemical energy to electrical energy for the charges until it is fully depleted.
Chemical energy stored in the battery is released in chemical reactions inside the battery and converted to electrical energy.
An analogy to the role of an emf source in a circuit.
Definition of e.m.f.
Electromotive force, emf =
= energy supplied by batteries per unit charge to circuit (V)
Arrangements of e.m.f. sources
3 cells of 1.5 V each
Total e.m.f. = 1.5 + 1.5 + 1.5 = 4.5 V
Total e.m.f. = 1.5 + 1.5 - 1.5 = 1.5 V