• Dhanush kumar S

Electric power

Updated: Dec 1, 2020

We all know that our home appliances like television, refrigerator, washing machine are working only with the help of #electricity. And we all would have noticed that every month, a person from the electricity board will visit our home and calculate our electricity bill for that respective month. Have you ever wondered how that is calculated? It is by determining the amount of energy utilized by various appliances in our home. This can also be said as the electric power consumed by machines.


#Power can be simply defined as the amount of energy consumed to perform an operation. If #electrical energy is involved in performing an operation, then it can be measured in terms of electric power. In this article, we are going to discuss in details about the electric power, the way of measuring it, its types, and various transformations of electric power.


What is electric power?


Technically, electric power can be defined as the rate at which electric energy is transferred through an electric circuit per unit time. Electric power is usually produced by electric generators and can be transferred to various domestic houses and industries by using an electric power grid. Transmission lines made up of copper or steel alloy cables are used to transfer the electric power over a long distance.


Transmission of electric power

Electric power can be transformed into various kinds of energy depending on which electric circuit the carriers are traveling through. For example, when the carriers pass-through a circuit of the light bulb, the filament of the bulb gets heated which gives us light. The amount of heat generated represents the amount of electric power dissipated.


Measurement:


Electric power is measured based on the SI unit Watt. The unit is named after Scottish scientist James Watt. One watt is defined as a derived unit of 1 joule per second and used to measure the rate of energy transfer.


P = Work done by an electric current / time i.e.


P = V * ( Q / t ) = V * I


where Q is electric charge in coulombs, t is time in seconds, I is the electric current in amperes, V is the voltage in volts. Watt can be defined in both mechanically and electrically. Mechanically defining, one watt is the rate at which work is done when the velocity of the object is constant at one meter per second against a one-newton opposing force.


Electrically speaking, one watt is the rate at which work is done when one ampere current flows through a network that has an electric potential difference of about one volt. Commercially, electric power is measured in kilowatt.


1 kilowatt = 1000 watt.


By using ohm's law, we can derive various formulae for calculating electric power. W=VI can be modified into W= V^2/R, and W= I^2.R


Types of electric power


Electric power can be classified into 2 types, based on the type of current involved in the work done. They are DC power and AC power. DC power is merely defined as the product of DC voltage and current. The required DC voltage can be generated with the help of fuel cells, batteries, and generator.

DC power

AC power can be defined as the amount of work done with the help of DC voltage. AC power can be divided into apparent power, active power, and reactive power.


Apparent power is also known as idle or useless power. It can be defined as the product of RMS voltage and RMS current.

S= Vrms * Irms


Active power is the real power dissipated across the circuit resistance. It can be defined as the product of peak voltage, peak current, and impedance phase angle between voltage and current

P=V max * I max * cosϕ


Reactive power is the power developed in the circuit reactance and measured in volt-ampere reactive.

Q=V max * I max * sinϕ

AC power

The relation between apparent power, active power, and reactive power can be defined as S^2= Q^2 + P^2. The ratio of active power and apparent power is known as the power factor and the value of power factor lies between 0 and 1.


Devices:


As mentioned above, electric power can be transferred into different forms and this operation is performed by the components in the electric circuits. They are active and passive devices.


In a device, if the electric charges are moved by an external force from low electric potential to high electric potential, mechanical or chemical kind of energy can be converted into electric potential energy. These types of devices are called active devices or power generators. For example, batteries that convert chemical energy in them to electrical energy. Similarly, windmills that convert the mechanical energy to electrical energy. Depending on the current flowing through them, the devices can be either source or load.


In certain devices, when the electric charges move from high electric potential to low electric potential, the potential energy of the charges is being converted into kinetic energy. These types of devices are called passive devices or loads. These devices consume electric energy and convert them into other forms of energy. For example, electric heaters consume electric current and produce heat in their filaments so that the water gets heated.


Applications of electric power:

  • Electricity produced by various methods is stored in power stations and transmitted to various locations using the transmission grid. This power is used for various commercial, industrial, and domestic purposes

  • Electrical energy is used in the production of electric arc furnaces and in the extraction of metals such as aluminum, steel.

  • In telecommunication and broadcasting of tv programs, electric power is essential.

  • Electric motors consume electricity in order to pump water for both irrigations and domestic houses.

  • Street lights, signboards, stop lights uses electric energy for their functioning.

  • Air conditioning in all our home consumes electric energy and keep our houses warm or cold depending on the climate.


See also:

  1. Capacitors & capacitance

  2. Resistors & resistance

  3. Transistors

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