Electric Generator and Electromotive Power

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Electric generators are devices that convert energymechanics, chemistry or even. solar in energyelectric. The energy produced by generators can be used to power electrical circuits. See below some examples of generators:

→ Batteries


→ Batteries

Car battery

→ Diesel-powered generators

Diesel-powered generator

→ Hydroelectric Power Plants

hydroelectric plant

→ Solar plants (photovoltaic plates)

Solar boards

→ Wind power plants

wind energy

→ Nuclear Power Plants

Nuclear energy

The phenomenon used by some of the above generators to transform mechanical energy into electrical energy is called electromagnetic induction.This process consists of changing the magnetic field flux over a conducting loop, thus promoting the emergence of a alternating electrical current.

See too: The Discovery of Electromagnetic Induction

At platesphotovoltaic, in turn, are capable of transforming the energy present in the electromagnetic waves in electricity through the photoelectric effect.

electromotive force

THE strengthelectromotive (FEM) corresponds to the entire electrical potential that can be produced by a generator. When connected to a circuit, part of the energy generated is

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dissipated in the form of heat due to the formation of a electric current inside. This phenomenon, called joule effect, it happens because the generators have a certain internal resistance, therefore, there is no perfect generator.

Electromotive force can also be understood as the amount of electrical potential energy that generators supply to each unit of electrical charge:

Electromotive force - 2

We can calculate the electromotive force produced by a generator using the following equation:

electromotive force

AND – electromotive force [V]
U – usable electrical voltage [V]
ri– generator internal resistance [Ω]
i – electric current [A]

The equation above suggests that part of the produced energy by a generator (AND) é used to call electronic devices (U), and another part is dissipated(ri.i). Through the electromotive force equation, it is possible to deduce the characteristic equation of generators, that provides us with the usable voltage(UU) by a circuit powered by a real generator:

Equation of generators

Mind Map: Generators

Mind Map: Generators

*To download the mind map, Click here!

Representation of the generator in the circuit

Generators are usually represented in circuits, whose diagram is shown below:


In generators, the electric current (in the conventional sense) must always flow from the smaller to biggerpotentialelectric, demonstrated by barlittle (-) and for big bar (+), respectively. This representation indicates that the electrical current gains energy when passing through the generator. The resistance ri shown in the circuit is the internal resistance of the generator.

Characteristic curve of generators

The characteristic curve of generators is a straightdownward at the firstquadrant of flatCartesian. Represents the voltage drop inside the generator and can be understood as follows:

  1. If the current formed by the generator is null (i = 0), then no energy will be dissipated. Therefore, all the voltage produced will be the electromotive force itself (U = E).

  2. If the generator is short-circuited, connected directly to the positive and negative terminals by a wire without resistance, the maximum possible current will be produced. If that generator is connected in a circuit and produces such current, its internal resistance will consume all the energy produced. In this way, the potential established by the generator will be null (U = 0). Watch:

Characteristic curve of generators

AND – electromotive force [V]
ri– generator internal resistance [Ω]
icc – short-circuit electrical current [A]

Through the 1st law of Ohm, we can use the information contained in the characteristic curve of generators to calculate their internal resistance. Watch:

Calculation of the generator's internal resistance

See too: Ohm's law

Electric power in generators

Electric power is a scalar quantity measured, usually in watts (or derived units). Represents the rate of change of electrical energy as a function of time. In generators, there are three types of electrical power:

  • Total electrical power: corresponds to all the electrical power produced by the generators. It is given by the equation:

full power
  • Usable electrical power: electrical power available to the electrical circuit. It can be calculated using the following equation:

useful power
  • Dissipated electrical power: electrical power consumed by the Joule effect due to the passage of electrical current through the internal resistance of the generators.

    dissipated electrical power

Therefore, the energy balance in generators can be synthesized by the following equations:

Energy balance in generators

Generator income

The income of generators is a greatnessphysicsdimensionless which indicates the generator capacity in transforming some form of energy in electricity. The income of the generators is given by the reason between the potentialelectricuseful and yours strengthelectromotive:

generator income

By Me. Rafael Helerbrock

Source: Brazil School - https://brasilescola.uol.com.br/fisica/geradores-eletricos-forca-eletromotriz.htm


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