Potential Difference and Emf – In the previous section we have seen that when one end A of the conductor is connected to the positive terminal and its other end B is connected to the negative terminal of the battery then the potential of A becomes higher than the potential of B, an electric field is set up due to which the current flows from A to B. this flow of current is due to the motion of free electrons from B to A (fig. 16.4).
For continuous flow of current, it is essential that when the electrons after passing through the conductor reach the positive terminal A of the battery, they should be pumped from here to the negative terminal B through the battery. This transfer of electrons in the battery takes place due to a chemical process which produces the necessary energy for pumping the electrons. The amount of energy supplied by the battery in pushing one coulomb of charge (electrons) from its positive terminal to its negative terminal through the battery is known as the electromotive force (emf).
When a conductor is connected across the terminals of the battery, electrons begin to flow through it. During their flow, they face a resistance due to the collisions with the atoms present in the conductor. The energy supplied to electrons by the battery is utilized in overcoming this resistance and is dissipated as heat and other forms of energy. The dissipation of this energy is accounted for by the potential difference across the two ends of the conductor. Thus the emf in a circuit dives the energy supplied to unit charge by battery and the potential difference accounts for the dissipation of this energy into other forms as unit charge passes through the circuit.
