Question

give the significance of internal resistance of a EMF source

Answer 1

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.

ε = E/Q

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.

ε = I(R+)

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