In the previous text we have described how an e.m.f supplies energy to electrons in d.c. circuits and how resistors convert
this energy to heat as the electrons move around the circuit.
We defined voltage (E or V) as the ratio of energy to charge.
Therefore the energy supplied by an e.m.f, or the energy dissipated by a resistor, can be calculated using the voltage, current and the time period over which the energy was supplied or dissipated.
The energy dissipated by a resistor is given by:
In either case it is clear that: Energy = voltage x current x time.