- Practical circuits
- All sources of e.m.f have an internal resistance. This may be due to the wires for a power supply whereas for a cell its due to the chemicals within it.
- The reason for the heating effect in batteries is that some of the electrical potential energy of the charges is transformed to internal energy.
- E=I (R+r)
- V= E-Ir
- Internal resistance can be found from a graph of V against I.