D.C. DC electric circuits: calculation

DC currents are moving indefinite direction of a particle with a charge. In another way, current can be called quantities such as current or voltage, which are constant in both direction and value.

Consider its characteristics, application, andalso electric circuits of direct current. Let's answer the questions, how the electric circuit is investigated, as it is calculated for some others.

From plus to minus or vice versa?

In the source, electrons move from the minus onevalues ​​to plus. Despite the fact that everyone knows this, it is usually considered a direction from plus to minus. I wonder why? We are explained that this has happened historically. But is it really so? After all, this "history" was formed in some absolutely insignificant period of time.

In the direct current, the main lawsElectrical engineering: Ohm's law and the laws of Kirchhoff. The current was called earlier galvanic, because it was obtained as a result of a galvanic reaction. When electric current began to be carried into houses, there was a harsh debate over what kind of current to enter: constant or variable. "War" won the second, because it was less expensive. It is much easier to transmit over long distances due to easy transformation.

How to obtain a direct current

But the direct current did not disappear from the use. Electric DC circuits are found, for example, in batteries.

Current is generated by electromagneticinduction, after which the collector is rectified. Such a reaction produces a generator, where a direct current is also produced. Electric DC circuits can be transformed from a variable one through converters and rectifiers.

Application area

The application of this species is quite wide. In most home appliances, for example, in a computer modem, charging for a mobile phone, an electric kettle or a food processor, it's DC. Electric DC circuits are generated and converted on an automobile generator and any portable device. It operates all industrial engines, and in some countries even high-voltage transmission lines. Even in some medical devices it is used.

The DC current is safer, since a fatal event can occur when an electric shock is from 300 mA, and with an alternating current, even at 50-100 mA.

Electrical circuit

Communication is provided by all devices,due to which the transfer, distribution and transformation of thermal, electromagnetic, light and other types of energy information is carried out. The processes are described by such electromotive forces as current and voltage.

Basic elements of DC electric circuits

The main elements are receivers and sourcesenergy information, connected by conductors. In sources, various types of energy are converted into electrical energy. And in the receivers, on the contrary, the electricity goes into other types.

Chains, where the transformation, transmission and receptionelectric energy occurs at a constant value of voltage and current throughout the entire time, are called DC circuits. Where the process occurs with a variable value - AC circuits.

To calculate and research(laboratory work for these purposes usually serves), a replacement circuit is used, that is, an idealized circuit for real calculation. To get it, you need to replace all the elements of the circuit. Physical processes must be expressed in every mathematical description.

Resistive elements

The resistor is one of the receivers of the electrical circuit. It is characterized by an active resistance, which is measured in Ohms. Resistive resistances, or, as they are also called, are actively introduced into substitution circuits to take into account the transforming electromagnetic energy into other species.

Calculation of complex electrical circuits of permanentThe current is produced if the positive direction of all currents and voltages is set. Choose the direction of their node, which has a great potential for a node with a smaller potential.

With an independent resistance from the current resistorare called linear, and the electrical circuit is linear resistive. The current-voltage characteristic is expressed in terms of a linear function passing through the origin.

When analyzing such chains, the principle ofsimplification, consisting in replacing complex sections of the electrical circuit with simple ones. But the current and voltage should not change. Then the chain will fold to the simplest kind. The connected resistive elements must be parallel and sequentially converted.

Serial and Parallel Connection

With a series connection in all elements, the current has the same value. Here the voltage is determined by the sum of all the included resistances multiplied by I, that is:

U = (R1 + R2 + RN) I = RI.

When parallel connection is usedconstant voltage, but the current is the sum of the currents on each of the elements. Therefore, it can be represented as a product of the voltage by the equivalent conductivity of the active elements. And it, in turn, is equal to the sum of the conductivities of the elements. This is what constitutes direct current.

Electric DC circuits, in addition, contain voltage and current sources.

Sources of information

Independent voltage (EMF, current) fromthe resistance of the external circuit is called its source. The source of the EMF (voltage) is measured at idle, that is, where the current in the source is zero. In the replacement circuits, the resistor takes into account the thermal energy losses that are released from the source. If it is zero, and the current source is infinity, it is an ideal source. The real is always finite.

The external characteristics are as follows: for sources of EMF and voltage, the dependence arises from the current flowing, and at the current source - from the voltage at the terminals.

Real sources have linear and nonlinearsites. Let's consider methods of calculation of linear electric circuits of a direct current. They are described in Ohm's law for the complete chain, where I = E / (Rh + Rbh). Then U = E- RbhI. From these formulas, internal resistance and internal conductivity are derived:

• Rbh = ΔU / ΔI;
• Gbh = ΔI / ΔU.

Calculation of nonlinear electric circuits of a constantcurrent is produced on the basis of Kirchhoff's law. Calculation methods for linear and nonlinear schemes are different. Therefore, the latter are not considered in the framework of this article.

Linear measuring instruments

DC electric circuit capacitancecontains sources. And the instruments that measure it are: a voltmeter for measuring the voltage in the circuit section and an ammeter for sequential connection to the circuit. With a zero value of internal resistance and conductivity, the instruments are ideal.

The methods of inclusion become more understandable when considering them using a resistance measurement. By Ohm's law, R = U / I.

We know that real devices do not have zero value. Therefore, only two options for their inclusion are possible:

• the internal resistance of the voltmeter is several times greatermeasured ammeter - such that the reduction in voltage on it does not reduce the reduction in the measured resistance, and the voltage measured by the voltmeter should correspond to the operating range;
• the internal resistance of the voltmeter is commensurate with the measured resistance, and the ammeter is much less than the measured resistance.

Experiment and tasks for the test work

To measure voltage and current, the corresponding generators are used. The internal resistance is measured by means of switches.

The voltmeter and ammeter enter the block AB1.

Special measures are used to measure the resistance. In the source of the electromotive force, the internal resistance must be switched off.

In the recommended task, which should becontrol work, DC electric circuits are studied by determining the parameters of the source of the electromotive force, the current source, measuring the resistance, studying the inclusion of parallel and series resistances, VAC.