Electrical energy and power

Introduction to Electrical Energy

Think about your phone battery or the generator in your yard. When you switch on your bulb or fan, something is being used up to make those things work. That 'something' is Electrical Energy. It is what allows charges to move through your wires and do work for you, like cooling your room or grinding your pepper.

Simply put, it is the total work done by electricity over a period of time.

The SI unit for electrical energy is the Joule (J). We calculate it by multiplying the voltage (V), the current (I), and the time (t) in seconds. The formula is E = VIt.

Understanding Electrical Power

Have you ever noticed that some light bulbs are brighter than others? Or that an electric kettle boils water faster than a small immersion heater? This is because of Power. While energy tells us the total work done, power tells us how fast that work is being done. A high-power bulb uses up energy very quickly.

In simple terms, power is just energy divided by time.

The SI unit of power is the Watt (W). One Watt is equal to one Joule per second. You will see '60W' or '100W' written on the bulbs you buy at the market.

Important Power Formulas

We can calculate power using three main formulas depending on what we know in the circuit:

1. P = IV (Power = Current multiplied by Voltage)

2. P = I² R (Power = Square of Current multiplied by Resistance)

3. P = V² / R (Power = Square of Voltage divided by Resistance)

Worked Example

Let us look at a real situation. A small electric boiling ring is connected to a 240V NEPA supply. If the resistance of the heating coil is 48 Ohms, calculate the power of the boiling ring.

Step 1: Identify the given values. Voltage (V) = 240V, Resistance (R) = 48 Ohms.

Step 2: Choose the correct formula. Since we have V and R, we use P = V² / R.

Step 3: Calculate the square of the voltage. 240 multiplied by 240 = 57,600.

Step 4: Divide by the resistance. 57,600 / 48 = 1,200.

The power of the boiling ring is 1,200 Watts or 1.2 kilowatts (kW).