Electrical Energy and Power - Definition, Formula, FAQs

What is Electrical Energy?

Electrical Energy can be defined as the energy produced by the movement of electrons from one point to another. It is a type of kinetic energy as it involves the motion of charged particles. The movement of charged particles creates current or electricity.

S.I. Unit of Electrical Energy

The SI unit of electrical energy is the joule (J).

One joule is defined as the amount of energy used when a current of one ampere flows through a resistance of one ohm for one second. In terms of electrical power:

1 joule $=1$ watt $\times 1$ second

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How to Calculate Electrical Energy?

The formula to calculate electrical energy is:

$
E=P \times t
$
Where:

• $E$ is the electrical energy in joules (J) or kilowatt-hours (kWh),
• $P$ is the power in watts (W),
• $ t$ is the time in seconds (s) or hours (h).

Fundamental Concepts in Electrical Energy

1. Voltage (V): The electric potential difference between two points. It drives the flow of electrons in a circuit.
2. Current (I): The rate at which electric charges flow through a conductor, measured in amperes (A).
3. Resistance (R): The opposition a material offers to the flow of electric current, measured in ohms ( $\Omega$ ).
4. Power (P): The rate at which electrical energy is transferred or consumed, is called Power. It is measured in watts (W).

Examples of Electrical Energy

Here are some common examples of Electrical energy in everyday life:

• Lighting: Light bulbs use electrical energy to produce light energy that helps light homes, offices, and streets.
• Heating Appliances: Home appliances such as electric heaters, ovens, and water heaters directly utilize electrical energy to provide heat for cooking, heating rooms, or water respectively.
• Computers and Mobile Devices: Working on electrical energy in batteries or electrical outlets, laptops, smartphones, and tablets.
• Power Tools: Drills, saws, and other electric tools perform electrical energy to mechanical energy to build and repair works.
• Medical Equipment: These include MRI machines that use electrical energy to produce images of the human body, and X-ray machines that use electrical energy to detect sickness.

The below table describes the electrical Energy in the summarised form for easy understanding.

What is Electric Power?

Electric Power is defined as the rate at which work is performed in an electrical circuit. In simple words, we can say that electric power tells us how fast electrical energy is converted into another form of energy.

S.I. Unit of Electric Power

The standard unit of electric power is the watt (W).

Electric Power Formula

The formula to calculate electric power is:

$
P=V \times I
$

where:

• $P$ is the electric power in watts (W),
• $V$ is the voltage in volts $(V)$.
• $I$ is the current in amperes (A).

Electric Power can also be calculated using Ohm's Law. The formula to calculate Power using Ohm's law is:

$
P=I^2 \times R
$

or

$
P=\frac{V^2}{R}
$

where $R$ is the resistance in ohms $(\Omega)$.

Types of Electrical Power

In electrical engineering, power is defined as the rate at which electrical energy is consumed or converted into other forms of energy. Depending on its nature and usage in an electrical circuit, electrical power is classified into the following types:

1. Active Power (Real Power)

Active power is the power that is actually consumed in an electrical circuit to perform useful work such as lighting lamps, heating, or running motors.

It is measured in watt (W).

$
P=V I \cos \phi
$

2. Reactive Power

Reactive power is the power that is not consumed but continuously flows back and forth between the source and reactive components like inductors and capacitors.

It is measured in volt-ampere reactive (VAR).

$
Q=V I \sin \phi
$

3. Apparent Power

Apparent power is the total power supplied to the electrical circuit.
It is the combination of active power and reactive power.
It is measured in volt-ampere (VA).

$
S=V I
$

Applications of Electric Power

• Residential Use: Powering household appliances like refrigerators, televisions, and washing machines.
• Industrial Use: Operating heavy machinery and lighting large areas.
• Transportation: Powering electric vehicles and trains.
• Power Distribution: Measuring the power delivered by generators to the grid.

Numericals on Electric Power and Energy:

Question 1: A 100-watt bulb is used for 10 hours. Calculate the electrical energy consumed by the bulb in kilowatt-hours ( $\mathbf{( W h ) .}$

Solution:

$
\begin{gathered}
\text { Power }=100 \mathrm{~W} \\
\text { Time }=10 \text { hours } \\
\text { Energy }(\text { in } \mathrm{kWh})=\frac{\text { Power (in W) } \times \text { Time (in hours) }}{1000} \\
=\frac{100 \times 10}{1000}=1 \mathrm{kWh}
\end{gathered}
$

So, the electrical energy consumed is 1 kWh.

Question 2: An electric heater has a resistance of $20 \Omega$ and is connected to a 220 V power supply. Calculate the power consumed by the heater.

Solution:

Using the formula $P=\frac{V^2}{R}$,

$
\begin{gathered}
V=220 \mathrm{~V} \\
R=20 \Omega \\
P=\frac{220^2}{20}=\frac{48400}{20}=2420 \mathrm{~W}
\end{gathered}
$
The power consumed by the heater is 2420 W.

Question 3: A device operates on a 5 A current and 12 V voltage. Calculate the power consumed by the device and the energy consumed if it runs for 2 hours.

Solution:

Step 1: Calculate power.

$
P=V \times I=12 \times 5=60 \mathrm{~W}
$
Step 2: Calculate energy in kWh.

$
\text { Energy }=\frac{P \times \text { Time }}{1000}=\frac{60 \times 2}{1000}=0.12 \mathrm{kWh}
$
The power consumed is 60 W, and the energy consumed is 0.12 kWh.