__Power supplied and power dissipated__

In the given diagram, as the current (I) flows through the resistor, electric potential (V) between the two points drops by dV thereby decreasing the potential energy (U). The small amount of charge that moves within a small interval of time (dt) is given by (dq=i * dt). Therefore, the small change in potential energy can be written as

Power is the rate of change of potential energy which we can write as

Therefore using the above equation gives

**dU/dt**.Therefore using the above equation gives

As electrons flows through the resistor, collision of electrons with the molecules of the resistor can not be avoided. Collision of electrons with molecules of resistor will convert mechanical energy of electrons into electrical energy leading to dissipation of power at the resistor. We can use the equation V = IR (applicable at constant temperature) and equation (i), derived above, to get the formula for power dissipated at the resistor as