Commercial Unit Of Electrical Energy | What is Electrical Energy?

In this article, we will discuss the Commercial Unit Of Electrical Energy and What is Electrical Energy. Dear Student Wellcome To Academy24x7 is a Global Online Learning Platform. Here You Can Find Your Engineering Academy Study Related Question and answer with Us.

Today We Cover In This Post, the Most Searchable Question in Google. from Electrical Engineering Department. The Question is Commercial Unit Of Electrical Energy and What is Electrical Energy?

Energy is the capacity to do the work and it is defined by how much time the work is done or applied. energy can exist in different forms like thermal energy, kinetic energy, nuclear energy, etc. you must hear those previous lines before and it’s right but in electricity, we must understand the energy beyond that because here charge particles are flowing inside the wire and current, voltage, and power is produced along with various effect like magnetic, electrostatic, etc. So the definition of energy is a little bit different in the case of electricity…

What is an Electrical Energy?

Electrical energy is an important concept in science and also in engineering, yet it is frequently misunderstood by people. Electrical energy is the energy produced by the movement of a certain charge particle. this flow of charge is called current. so to flow current from one point of a circuit to another point of the circuit so work has to be done and the total amount of work is called electrical energy. The rate at which the electric power is transferred is called electrical power. some examples of electrical energy are car batteries, the lightning during thunderstorms, and Electric eels that generate electrical energy and use it against predators for defense.


Electrical potential energy or kinetic energy of the charged particles makes the electrical energy. In general, it is the energy that has been converted from electric potential energy. or in simple language, you can say the energy is generated by the movement of electrons from one point to another point.

If you have read the above lines, you must get the concept of electrical energy and now we can jump into our actual topic is commercial units of electrical energy but before that let me tell you what we are going to cover in this post……..

  1. The formula of Electrical Energy.
  2. Units of Electrical energy and Power.
  3. Relation between electrical energy and mechanical energy.
  4. Why do we study Commercial Units Of Electrical Energy?
  5. Relation between the commercial and SI unit of Electrical Energy.
  6. problems based on Electrical energy.

Formula Of Electrical Energy :

To understand the formula let me consider a battery cell as an electrical circuit and try to derive the formula for the cell. A cell has two terminal positive terminal and a negative terminal .negative terminal has the excessive of electron and if current goes from positive terminal to negative terminal then the electron motion will be negative to positive. Let us take the positive terminal as terminal A with potential VA and the negative terminal as Terminal B with potential VB . and here always VA is greater than VB.

The potential difference between A and B is given by

V = VA –VB > 0

Mathematically, electric current is the rate of flow of charge through the cross-section area of a conductor.

Thus, it is given by I = ∆Q/ ∆t where I is the electric current and ∆Q is the quantity of electric charge flowing through a point in time ∆t.

The potential energy of charge Q at A is Q VA and at B, it is Q VB. So the change in the potential energy is defined as…

∆Upot = Final potential energy – Initial potential energy

= ∆Q [VB – VA ] = –∆Q V

= –I V∆t ( I = ∆Q/ ∆t)

If we take the kinetic energy of the system into account, it would also change if the charges moved without collision. This is to keep the total energy of the system unchanged. Thus, by conservation of total energy, we have:

∆K = –∆Upot

Or ∆K = I V∆t > 0

Thus, in the electric field, if the charges move freely across the conductor, there would be an increase in the kinetic energy as they move.

Units of Electrical Energy

Two basics unit of electrical energy are jule and Watt-second. When one ampere current is flowing in a circuit for one second  whose potential difference is one volt then the energy applied is called one jule. The commercial unit of electrical energy is kilowatt-hour which is also known as Board of trade unit(B.O.T).

1 kwh = 1000 × 60 × 60 watt – second
1 kwh = 36 × 105 Ws or Joules

one kwh is called one unit.

Why we need Commercial Unit Of Electrical Energy ?

The SI unit of electrical energy is Jule represented by J . it is used in case of small system or circuit but, When large amounts of energy need to be expressed, commercial units of energy are required, and this is utilised in industries ,factories and even in our home electricity unit measurement.

Commercial Unit of Electrical Energy :

Kilowatt-hour is a commercial unit of electrical energy. One kilowatt-hour energy will be consumed by a machine when the machine constantly use one kilowatt power for one hour. It is represented by KWh.

Relation between the commercial and SI unit of Electrical Energy :

To get the the relation we have to use the power equations . Power is nothing but the energy used in per unit time . i.e., electrical energy divided by time is equal to electrical power. SI unit of power is Watt and represented by W.

P = E ⁄ t


  1. P = the power generated
  2. E = total energy consumed
  3. t =the time for which power applied

if we write the formula in terms of energy then it will look like……

E = P t

 the Kilowatt-hour in terms of above formula…….

Consider the power equal to 1 kW and time equal to 1 h.

E = P t

1 kW h = 1kW × 1 h

1 kW h = 1000 W × 1 h

1 kW h = 1000 (J / s) × 3600 s

1 kW h = 3.6 × 10J.


Hencce, we can say 1KWh is the energy that consumed when 1kw power  applied or consumed for an hour. When it used to represent the energy it , it does not refer the amount of kilowatt energy that used in every hour rather its the It’s just a unit of measurement that represents the amount of energy used . Suppose a 1000 watt bulb is left on for one hour then it will consume 1Kwh. but in case of a 10 watt bulb it would take 100 hour to consume 1kwh.

Although the kilowatt-hour is not a recognized system unit, we make it for widely used electrical applications. Commercial applications  and household applications have different rates of charge but both are measured in kilowatt-hour. In general commercial appliances (Factories,industries ,etc) have a higher rate of charge compare to residential used .


Problems based on Unit Electrical energy

Problem 1: Define the relation between Joules and  1 unit of energy.

answer :

1 unit of energy is means 1 kW h.

1 kW h = 1000 W  × 1 h

            =1000 (J / s) × (60 × 60) s

            = 3600000 J

            = 3.6 × 106 J.

Problem 2: Why Kilowatt-hour is used as the commercial unit of energy?

Answer : If you read the post carefully ,you have the answer. SI unit of electrical energy is joule. one jule is nothing but the amount of energy that consumed when one watt power conststantly consumed for one second.but in real life if we want to calculate power for large applications like energy consumed of a family over the period of one year then the calculation will be super lengthy .So to get a simple calculation we convert watt to kilowatt and second to hour as we do that ,unit becomes kilowatt-hour.

Problem 3: Name the unit used in selling electric energy to consumers. An electric motor takes 10 A from a 110 V line. Determine the power of the motor and energy consumed in 3 hrs. Calculate the cost of electric energy for the month of June at a rate of Rs. 9 / unit.


Kilowatt-hour (kWh) unit is used in selling electric energy to consumers.


Current drawn to motor, I = 10 A

Voltage across the motor, V = 110 V

Time for energy is consumed, t = 3 h

Power generated by motor, P = V I

= 110 V × 10 A

= 1100 W

Energy consumed by motor, E = P × t

= 1100 W × 3 h

= 3.3 kW h


Energy consumed, E = 3.3 kW h

Cost of energy per unit, c = Rs. 9 ⁄ unit

Number of days, n = 30

Total Cost, C = E c n

= Rs. (3.3 × 9 × 30)

= Rs. 891.00

Hence, selling unit of energy is Kilowatt-hour, power generated by motor is 1100 W, energy consumed by motor is 3.3 kW h, and cost of energy is Rs. 891.

Problem 4: Convert 108000 J of energy into kilowatt-hours.

Answer :

we know, 3.6 × 106 J = 1 kW h

So, 1 J = (1 ⁄ 3.6) × 10-6 kW h

Therefore, 108000 J = (108000 ⁄ 3.6) × 10-6 kW h

                             = 3× 10-3 kW h (and).



I hope you have found the answers to all your questions through this post. About Commercial Unit Of Electrical Energy  After that, if you have any questions, you can comment in our comment box.

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