4Electromotive force and internal resistance of current source.

Electromotive force

The electromotive force  E of the source is the energy supplied to unit charge by the cell.

When a source of electrical energy is connected across a resistance R,it maintains a steady current through the resistance.Battery make the positive charge to flow in the external circuit.

Suppose a charge Δq passed through the circuit in time Δt.This charge enters the  cell at its lower potential (negative terminal) and leaves at its positive end ( positive terminal),then the source must do work ΔW on the charge Δq in taking it to the positive terminal which is at higher potential.

Thus ,the emf of the source is defined as” the energy supplied to unit charge by the cell.”

E = Energy/unit charge

or

E = ΔW/Δq

The above relation is the electromotive force formula.SI unit of emf is Joule/Coulomb which is equal to volt.

What is Potential Difference in physics?

Potential difference across the two points of a conductor causes the dissipation of electrical energy into other forms of energy as charges flow through the circuit.

When one end A of a conductor is connected to the positive terminal and its other end B is connected to the negative terminal of the battery, then the potential at A becomes higher than the potential at the B.

This causes a potential difference between the two points of the conductor. The flow of current continues as long as there is a potential difference. The agency which provides the potential difference for the steady flow of current in the copper wire is the battery. As the current flows from higher potential to the lower potential through the conductor, the electrical energy (due to the current) is converted into other forms (heat and light etc.).

When current flows through the conductor, it experiences a resistance in the conductor by collisions with atom of the conductor. This energy supplied by the battery is utilized in the 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 light bulb.