A Walk-Through Electrical Power, Energy, and Work


I am Suhas Ghatnekar, I live in PUNE city of Maharashtra state, INDIA.
I am an Electrical engineer, and a professional in the field of diesel power generation,
I have tried to compile basic information about Power Generation for the benefit of the people who want to know All about Power and Power Generation.
This is my first post on power generation. I am trying to keep the post as simple as possible.
In this post I will walk you through – What is Power, Energy, Work, their correlation and Units of measurement, Different types of Power, Type of Electric Power, and a brief history of Electrical Power in India.

What is Power?

The word Power we hear often especially when we refer to electricity.
Power comes from the Latin word “potere”, which means “to be able.”
As a normal practice if we ask Google “what is Power?” Google says,
Power is-

  • the ability or capacity to do something or act in a particular way.
  • the capacity or ability to direct or influence the behavior of others or the course of events.
  • energy that is produced by mechanical, electrical, or other means and used to operate a device.
  • supply to a device with mechanical or electrical energy.

In everyday life Power has a wide range of meanings, depending on the context.

In general Power is-

  • Physical Power
  • Leadership Power
  • Knowledge Power
  • Mind Power
  • People Power
  • Brain Power
  • Mechanical Power
  • Electrical Power

There are various types of  Power but in this post we will be discussing Power in Physics / Science – (Electrical / Mechanical)

In physics, power is the amount of energy transferred or converted per unit time.

In physics, power is the rate of doing work, or the amount of energy transferred per unit time.

Power is defined as the rate at which work is done upon an object. Power is always dependent on work done and is a time-based quantity.

The formula for power is-

Power = Work / time      

P = W / t
The unit for standard metric work is the Joule and the standard metric unit for time is the second,
so the standard metric unit for power is a Joule/second, defined as a Watt and abbreviated W.

It has no direction, and hence Power is a scalar quantity, and the SI unit of power is Watt (W) which is joules per second (J/s). 

In the International System of Units, the unit of power is the joule per second (J/s), known as the watt, in honor of James Watt,
the eighteenth-century developer of the steam engine condenser.

Watts are defined as 1 Watt = 1 Joule per second (1W = 1 J/s) which means that 1 kW = 1000 J/s.
A Watt is the amount of energy (in Joules) that an electrical device (such as an electric bulb) is burning per second.
So, when a 60W bulb is turned on, it is burning 60 Joules of energy every second.

It’s very common to see “watts” preceded by one of the standard SI prefixes: microwatts (µW), milliwatt (mW), kilowatt (kW), megawatt (MW), and gigawatts (GW), are all common depending on the situation.

Prefix Name Prefix Abbreviation Weight
Nanowatt nW 10-9
Microwatt µW 10-6
Milliwatt mW 10-3
Watt W 100
Kilowatt kW 103
Megawatt MW 106
Gigawatt GW 109

In physics work, energy and power are interrelated.
Let us understand what work and energy are and how power is related to them.

What is Work?

In physics, work is the process of energy transfer to the motion of an object via application of a force, often represented
as the product of force and displacement.
Work = Force × Displacement = F × d

The SI unit of work is the joule (J)

What is Energy?

Work and energy can be considered as two sides of the same coin. Work done is generally referred in relation to the force applied while energy is referred in relation to the other factors such as heat. 

In simple words, Energy is the strength required for sustained physical or mental activity.

In physics, it is defined as the capacity to do work, such as the capacity to move an object by the application of force.

Energy exists in many forms and is expressed in multiple units.

The SI unit of energy is joules (J), it is named in honour of James Prescott Joule.

Energy exists in different forms in nature, like Heat, Light, Magnetic, Chemical, Mechanical, Electrical, Nuclear and many other.
All forms of energy are either kinetic or potential.
The energy in motion is known as Kinetic Energy whereas, the energy stored in an object is Potential Energy.

Energy is governed by the Law of Conservation of Energy.


What is the Law of Conservation of Energy?

The law of conservation of energy states that, 
energy can neither be created nor be destroyed, it can only be transformed from one form to another.

In everyday life many of us seem to consider Energy and Power to be the same.

One cannot be blamed for finding similarity between energy and power as they are interrelated.

Energy is the ability to do work, while Power is its measurement.

Energy is what one delivers, and Power is the rate at which it is delivered.

Power (Mechanical)

What is Mechanical Power?

We have seen Power in physics, is a measure of the rate at which work is being performed over time. The word “mechanical” is merely descriptive; it indicates that the power is associated with a machine.

Power in mechanical systems is the combination of Forces and movement.

You can find mechanical power in use everywhere in the modern world. For example, just think of car drive, it used energy, either from fuel or a battery, to move an interconnected series of mechanical components – axles, gears, belts and so on until, finally, that energy was used to spin the wheels and move the vehicle forward.

The mechanical power formula uses the same fundamental laws of physics that are used for other forms of power.

Mechanical power is often measured in horsepower, although its sometimes measured in watts

James Watt while marketing his newly invented Steam engine to the customers using work horses, had to figure out mathematical way to equate horses to engine, to show how his steam engine could complete the work of multiple horses.

Thus, the term horsepower was invented.

James Watt determined that a work horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute).

The wheel was 12 feet (3.7 m) in radius; therefore, the horse traveled 2.4 × 2π × 12 feet in one minute.

James Watt determined that the horse could pull with a force of 180 pounds-force. So,

James Watt defined and calculated the horsepower as 32,572 ft⋅lbf/min, which was rounded to an even 33,000 ft⋅lbf/min.

The mechanical power is sometime measured in PS or Pferdestärke (horse-strength in German), Although PS replaced by kW in 1992, as the EU’s ‘legal’ measurement of engine power but still commonly used by many car makers. One PS is about 98.6% of a brake horsepower – the two are virtually interchangeable, and PS is sometimes referred to as ‘metric horsepower ‘.

The common and traditional measure is horsepower (compared to the power of a horse). Being the rate of work, the equation for power can be written:

power = work / time

One horsepower is needed to lift 550 lbs by 1 ft. in 1 second.
One metric horsepower is needed to lift 75 kilograms by 1 meter in 1 second.

Power (Electrical)

What is an Electrical Power?

Electrical power is the rate at which electrical energy is converted to another form, such as motion, heat, or an electromagnetic field.

In physics, Electric power is the rate, at which electrical energy is transferred by an electric circuit per unit of time. The SI unit of power is the watt, i.e., one joule per second. 

Definition of Electrical Power

Electrical Power is defined as the rate at which work is done on an electrical system. As we have discussed recently that doing work generates energy, and therefore power can be given as the rate of consumption of electrical energy.

Definition of Electrical Energy

Electrical energy is the energy generated because of the potential difference in a circuit that causes current to flow through it. Electrical energy is measured in kWh (kilowatt-hour)
In simple words, Electrical energy is defined as the overall work done in an electrical circuit.
Energy specifies the amount of work done to move an object, and in an electrical circuit, electric charges show movement. The work done on the electric charges to make a movement is known as electrical energy.
Electrical energy and electrical power are the two major terms associated with electrical and electronics systems.

Electrical energy and electrical power are the two major terms associated with electrical and electronics systems.

Energy is denoted by E while electric power is denoted by P.

The fundamental difference between electrical energy and electrical power is that Electrical energy defines the energy generated due to the movement of charge carriers in a conductor. While electrical power specifies the rate of consumption of electrical energy by a device.

In our day-to-day life, we often come across the term “Electricity” for example Electricity Bill, Electricity failure, etc.

Electricity is a very general term that we use when we refer to electrical power generated, transmitted, and distributed to our household.

The Greeks first discovered electricity about 3000 years ago. The word electricity derived from the Greek word “elektron”, which means amber. Amber is the yellow, fossilized rock you find in tree sap. The Greeks found that if they rubbed amber against wool, lightweight objects (such as straw or feathers) would stick to it.


In this blog post, I have walked you through the basics of Power, Energy, Work, and Electrical Power.
Now that you have understood what Mechanical Power and Electrical Power is, it will help you to know What is Electricity. One cannot see an electricity with human eyes and hence it is mysterious, complex, and dangerous. Electricity can hurt you if you touch it.

In this post, I have tried to compile all freely available information on various internet sites, so ultimately you do not need to spend your time searching for it.

Now next in the series on Power Generation I will post about electricity and its types.

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If so, please share it with your friends and colleagues or share it on Twitter or Facebook. This will help me improving my blog post readership. Thank you!!

Suhas Ghatnekar
Suhas Ghatnekar

The author is an Electrical engineer from the National Institute of Technology Rourkela India, an enterprising techno-commercial professional in the
field of diesel engines and diesel generators.

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