In this lecture we will try to understand the power and energy in circuits elements, which we have recently studied.

Resistors

We already know that resistor is a passive device . The power across resistor is given by

We can calculate the value of power and energy for both constant and time variable values .One must remember that resistor always dissipate power in form of heat . An example is heater , water rod

Energy Delivered to the resistor .

Similarly in previous discussion we have already discussed that if we take an integral of power with respect to time , we get a new term “Energy”

Energy

Energy absorbed by a resistor is

As resistor is a passive element , resistor can not supply energy , and always absorb energy . Same phenomena can be showed using , VI characteristic of curve.

The V- I Characteristic of resistor always lies in 1 and 3rd quadrant , which means power will always be greater than zero or positive. Hence we know positive sign represents power absorption phenomena.