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How to Calculate Electrical Power (With Simple Examples)

Introduction

Electrical power is an important basic topic for every Electrical Engineering student. It is used to measure how much energy is used by an electrical device or circuit. Knowing how to calculate electrical power helps you understand electrical appliances, machines, and circuits in real life.

In this article, you will learn the simple formulas to calculate electrical power for DC and AC circuits, with solved examples and practice questions.


What is Electrical Power?

Electrical power is the rate at which electrical energy is consumed or transferred by an electrical circuit.

Unit: The unit of electrical power is Watt (W).

1 kilowatt (kW) = 1000 Watts

1 megawatt (MW) = 1,000,000 Watts


Basic Formula for Electrical Power

For DC circuits:

P = V × I

Where:

P = Power in Watts (W)

V = Voltage in Volts (V)

I = Current in Amperes (A)

Electric Power Calculation
A simple lamp (bulb) is a common DC load


For AC Single Phase circuits:

P = V × I × cos(Ο†)

Where:

cos(Ο†) = Power factor (between 0 and 1)

In AC circuits, power factor is very important. It depends on the type of load.


Solved Example 1 (DC Circuit)

Example:

A lamp uses a voltage of 12V and draws a current of 2A. What is the power used by the lamp?

Solution:

P = V × I = 12V × 2A = 24W

So, the lamp uses 24 Watts of power.


Solved Example 2 (AC Circuit)

Example:

An electric motor runs on 230V, draws 5A current, and has a power factor of 0.8. Find the power used.

Solution:

P = V × I × cos(Ο†)

P = 230V × 5A × 0.8 = 920W

So, the motor uses 920 Watts of power.


Common Mistakes

✅ Forgetting to use the power factor for AC circuits.

✅ Mixing up DC and AC formulas.

✅ Not converting units properly.

Always check the type of circuit and the given data.


Practice Questions

Try to solve these problems to check your understanding:

1️⃣ A heater uses 240V and 4A current. Find the power.

2️⃣ A fan runs on 220V, 1.5A current, with a power factor of 0.9. Find the power used.

3️⃣ An LED light uses 5V and 0.3A. How much power does it use?

Write your answers in the comments or a notebook!


Conclusion

Electrical power calculation is a basic but important part of Electrical Engineering. You should always know the right formula for DC and AC circuits. Practice more questions and understand the concepts.


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