Electric Power and Electrical Energy

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Electric Power and Electrical Energy are two of the fundamental concepts in electrical and electronics engineering. Electric power is generally defined as the rate of work done in an electric circuit, while electrical energy is defined as the total amount of work done in a circuit over a certain period of time. Read this chapter to get a good understanding of these two important concepts.

What is Electric Power?

Electric power can be defined as the rate of work done in an electric circuit. In other words, the rate at which electrical energy is converted into another form of energy like light, heat, or motion in an electric circuit is called electric power.

Electric power basically gives idea about how fast electrical energy is being consumed in an electric circuit.

Formula of Electric Power

In an electric circuit, power is given as the time rate of work done, i.e.,

$$\mathrm{P = \frac{W}{t}}$$

From the definitions of voltage and current, we have,

$$\mathrm{V = \frac{W}{Q} \Rightarrow W = VQ}$$

$$\mathrm{I = \frac{Q}{t} \Rightarrow t = \frac{Q}{I}}$$

Substituting the values of W and t, we get,

$$\mathrm{P = \frac{VQ}{\left(\frac{Q}{I}\right)} = VI}$$

$$\mathrm{\therefore \text{Electric Power } P = V \times I}$$

Unit of Electric Power

The unit of electric power is Joule per Second (J/s). Where,

$$\mathrm{1\ \text{Joule per second} = 1\ \text{Watt}}$$

Watt (W) is the SI unit of electric power.

Larger units of electric power are kilowatt (kW) and Megawatt (MW).

$$\mathrm{1\ \text{kW} = 1000\ \text{Watt}}$$

$$\mathrm{1\ \text{MW} = 1{,}000{,}000\ \text{W}}$$

What is Electrical Energy?

Electrical energy can be defined as the total amount of work done in an electric circuit over a certain period of time. In other words, the total amount of electric power consumed over a certain period of time in an electric circuit is called electrical energy.

Thus, electric energy provides the amount of electricity used in a circuit over time.

Formula of Electrical Energy

From the definition, it is clear that amount of power consumed over time is called energy, thus,

$$\mathrm{W = P \times t}$$

Or,

$$\mathrm{W = V I t}$$

Unit of Electrical Energy

The SI unit of electrical energy is Joule (J). But in practice, electrical energy is measured in Watt-Second (Ws).

Other practical units of electrical energy are Watt-hour or kilo-Watt hour (kWh).

$$\mathrm{1\ \text{kWh} = 1000\ \text{Wh}}$$

$$\mathrm{1\ \text{kWh} = 1\ \text{Unit}}$$

Electricity Bill Calculation

Electricity bill calculation is nothing but calculation of electrical energy consumed over a certain period of time. Let us understand this with the help of an example.

Consider a fan of 60 Watt runs for 8 hours per day. Then, monthly energy consumption by this fan will be,

$$\mathrm{W = P \times t}$$

$$\mathrm{\Rightarrow W = \frac{60 \times 8 \times 30}{1000} = 14.4\ \text{kWh}}$$

Conclusion

In conclusion, power and energy are crucial for designing and analyzing electrical systems. Electrical power helps in understanding how fast electricity is consumed in an electric circuit, while electrical energy helps to calculate how much electricity will the circuit consume over time. Both these concepts pave the foundation for understanding advanced concepts in electrical and electronics engineering.