Let's discuss DC electric power
We know that current and voltage are two basic parameters of a circuit
Electric power is the product of current and voltage. Electric power is another essential parameter of an electrical circuit element
All of us have seen that a 100 watts electric lamp gives more light than a 60 watts electric lamp
If we apply voltage V, volts across a circuit element and for that if current flowing through
the element is I ampere, then the power consumed by the element is V into I watts
Let us examine how electrical power is the product of current and voltage
Suppose the element is a resistor. Let us assume dW is the energy consumed by the resistor during time dt
We know that power is rate of energy consumption with respect to time
This means power P equals to dW dt. This equation can be rewritten as P equals to dW dQ into dQ dt where dQ is the incremental
electrical charge. Again we know that dW dQ is voltage V and dQ dt is current I
So it is proved that electrical power is the product of voltage and current
We have discussed only about the power consumption in a circuit element which is resistor
But there are many circuit elements which can deliver electrical power to the circuit
These are battery generator like elements. They should be a method of representing the power so that we can understand the power
is consumed or delivered by the element. Whenever the current enters in a circuit element through the terminal of positive polarity
of the voltage across the element, then the power in the element is consumed
The consumed power is represented by a positive sign. Whenever the current leaves from a circuit element through the terminal of positive polarity
of the voltage across the element, then the power in the element is delivered to the circuit
The delivered power to the circuit is represented by a negative sign
Hope you got a basic idea of electrical power. Thank you