Study Material

Closed electrical circuit

We explain what a closed circuit is, its characteristics, components, symbols and we give several examples

Simple closed circuit, consisting of a source (batteries), two resistors in the form of bulbs and a closed switch that allows current to flow through the entire circuit

What is a closed electrical circuit?

closed electrical circuit is one in which the current has a continuous path through which to flow. This is a necessary condition for a current flow to occur, since a broken or cut wire prevents electrons from circulating through all elements of the circuit. what is closed circuit

In a simple circuit such as the one where a light bulb is turned on by a battery, the current flows through the light bulb only when the circuit is closed, otherwise the current would not circulate and the light simply does not turn on. what is closed circuit

A switch is used to control the flow of current through the circuit, with which the current is interrupted or diverted at will. There are several types, the simplest consists of two metal contacts, joined or separated at convenience through a mobile element. When the contacts are apart, the current is interrupted and when they are joined, the current flows. what is closed circuit

Every time the lights are turned on at home, in the car or an appliance that runs on electricity is turned on, numerous circuits are closed so that the current flows and does the corresponding work to achieve the desired effect. what is closed circuit

Characteristics of a closed circuit

-The operation of the circuit depends on a source of energy, known as emf (electromotive force), which can be direct or alternating.

-The closed circuit must provide the electrons with a complete path, without interruptions, so that they can circulate through each of the elements of the circuit.

-The wires that connect the different elements of the circuit are idealized, therefore, they lack resistance.

-In a direct current circuit, the direction of this is outgoing to the positive pole of the battery. what is closed circuit

-The current and voltage values ​​in each of the circuit elements are specified through Ohm’s law, when the circuit is resistive, in conjunction with Kirchoff’s laws, when it comes to more complex networks. what is closed circuit

Types of elements of a circuit what is closed circuit

They can be of two types:

  1. Assets
  2. Passives

The active elements  provide the energy, doing the work necessary for the electrical charge to set in motion. They are generators, which in turn can be of two types: voltage sources or current sources.

Then there are the passive elements , through which the electric current circulates. These elements consume current and in return produce an effect, such as a light bulb with a filament that lights up.

Components of a closed circuit

In general, an electrical circuit consists of the following components:

Generator what is closed circuit

It is responsible for producing and maintaining the electric current through the circuit, being able to be direct to the alternate. what is closed circuit

The direct generator is a simple cell or battery, while the alternates are called alternators.

Drivers what is closed circuit

They are very low resistance metal wires, usually made of copper covered with insulating plastic. Electric current moves through them, passing from one element to another in the circuit.

Receivers what is closed circuit

They are responsible for transforming the electrical energy that comes from the source into another kind of energy, for example, light, heat or movement. Examples of receivers are resistors, bulbs, filaments, capacitors, diodes, coils, and more.

Control elements

As their name suggests, they allow you to interrupt or redirect the flow of current through the circuit. They are the switches or switches. what is closed circuit

Protective elements

Protectors can be added to the circuits that interrupt the passage of current when it reaches a certain intensity, for example, fuses. In this way the circuit remains open, thus protecting the device and users. what is closed circuit

Schematics and Symbols

To facilitate the analysis of electrical circuits, diagrams and symbols are used, these offer a simplified representation of each of the circuit components. what is closed circuit

There are many symbols, one for each type of element, in the following image there is a small sample with the most used:

Symbols
The most common symbols used in electrical circuits.

By means of symbols, any circuit, even the most complex ones, can be schematized. In the circuit of the figure that appears at the beginning, the two bulbs connected in series are represented by two resistors and the scheme looks like this:

Resistive type closed circuit
Resistive type closed circuit, consisting of a battery, two resistors in series and a closed switch.

How does a closed electric work?

The operation of the closed circuit depends on the elements that compose it, for example, in the resistive circuit shown above, the light bulb lights up as soon as it is closed.

Instead, if one of the resistors is replaced by a discharged capacitor, the circuit becomes RC and the capacitor will charge to the source voltage.

When fully charged, it will be an open circuit. By disconnecting the switch and the source, and closing the circuit again, the capacitor temporarily produces a current, since it had previously stored charge.

In any case, the current is always taken from the positive terminal, as previously explained (see figure above).

The source is responsible for raising the potential of each charge q that is at that point, so its potential energy increases by an amount given by qε, where ε is the voltage supplied by the battery.

Then the charge q runs through the connecting wires, which are ideal, that is, without resistance, until it reaches a circuit element. If it is a resistance, as in the circuit in the figure, the load suffers a potential drop equal to I ∙ R 1 , where I is the intensity of the current.

Then it goes through another potential drop as it passes through the second resistance, this time from I ∙ R 2 until it reaches the negative terminal and from there to the positive terminal again, in this way, the load has made a complete journey around the circuit.

As energy is conserved, it is true that:

ε – I ∙ R 1 – I ∙ R 2 = 0

Worked example

In the circuit in the figure above, the values ​​of each element are:

1 = 430 Ω; R 2 = 128 Ω; ε = 9 V

  • a) What is the current through the circuit?
  • b) What current passes through each resistor?
  • c) Find the voltage drop across each resistor.

Answer to

The total current is what comes out of the battery. To find it, it is necessary to reduce the circuit to a single resistor. Since R 1 and R 2 are connected in series, the equivalent resistance R eq is their sum:

eq = R 1 + R 2 = 430 Ω + 128 Ω = 558 Ω

From Ohm’s law:

ε = I ∙ R eq → I = 9 V / 558 Ω = 0.01613 A

Answer b

Since the resistors are in series, the current is the same for both and equal to 0.01613 A.

Answer c

Applying Ohm’s law again:

1 = I ∙ R 1 = 0.01613 A ∙ 430 Ω = 6.935 V

Then V 1 = 9V− 6.935 V = 2.065 V

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