- #1

greypilgrim

- 547

- 38

Consider a simple circuit consisting of a voltage source ##U## and a load with resistance ##R##, e.g. a lamp or a motor. The current is given by ##I=U/R##. The number of electrons passing the circuit per second is ##n=I/e##. The power consumed by the load is calculated by

$$P=U\cdot I=U\cdot e\cdot n=\Delta E\cdot n\enspace,$$

where ##\Delta E=U\cdot e## is the (kinetic) energy an electron would gain traveling from the negative to the positive pole of the power source if there was no load.

In this computation, we assume the electron gives all its energy to the load and has kinetic energy zero when it arrives at the plus pole of the power source. But why is that? Why can't the electron maybe only lose half its energy to the load and still have kinetic energy when it enters the battery?