Power,Energy Power

Power,Energy

Power

Power is the time rate of expending or absorbing energy, measured in watts (W).

We write this relationship as

where p is power in watts (W), w is energy in joules (J), and t is time in seconds (s).

And also

The power p in above equation is a time-varying quantity and is called the instantaneous power.Thus, the power absorbed or supplied by an element is the product of the voltage across the element and the current through it.

If the power has a sign, power is being delivered to or absorbed by the element. If, on the other hand, the power has a sign, power is being supplied by the element.

Passive sign convention

Passive sign convention is satisfied when the current enters through the positive terminal of an element and p = +vi . If the current enters through the negative terminal, p = -vi .

Energy

Energy is the capacity to do work, measured in joules (J).

The electric power utility companies measure energy in watt-hours (Wh), where

1 Wh = 3,600 J