Direct current are particles with a charge moving in a certain direction. In another way, the current can be called such quantities as current strength or voltage, which are constant in both direction and value.
Consider its characteristic, application, as well as DC electric circuits. We will answer the questions of how the study of the electrical circuit is carried out, how it is calculated, and for some others.
From plus to minus or vice versa?
In the source, electrons move from a minus value to a positive one. Despite the fact that everyone knows about it, it is customary to consider the direction from plus to minus. I wonder why? They explain to us what has happened historically. But is it really so? After all, this “story” took shape in some completely insignificant period of time.
In direct current, the main laws of electrical engineering are in effect: Ohm's law and Kirchhoff's laws. The current was previously called galvanic, since it was obtained as a result of a galvanic reaction. When the electric current began to be carried out in the houses, there were tough debates about which current to introduce: direct or alternating. The “war” was won by the second, as it turned out to be less costly. It is much easier to transmit over long distances due to its easy transformation.
How does a direct current turn out
But the direct current did not disappear from use. DC electric circuits are found, for example, in batteries.
Current is generated by electromagnetic induction, after which the collector rectifies. This reaction produces a generator, which also produces direct current. DC electric circuits can be transformed from alternating ones due to converters and rectifiers.
Application area
The use of this type is quite wide. In most household appliances at home, for example, in a computer modem, charging for a mobile phone, an electric kettle or a food processor, it is direct current that works. DC electric circuits are generated and converted on a car generator and any portable device. All industrial engines operate on it, and in some countries even high-voltage electric transmission lines. Even in some medical devices it is used.
Direct current is safer, as a fatal outcome can occur with a shock from 300 mA, and with an alternating current - even at 50-100 mA.
Electrical circuit
Communication is provided by all devices, thanks to which the transmission, distribution and conversion of thermal, electromagnetic, light and other types of energy information is carried out. The processes are described by electromotive forces such as current and voltage.
The main elements of DC electrical circuits
The main elements are receivers and sources of energy information, connected by conductors. In sources, various types of energy are converted into electrical energy. And in receivers, on the contrary, the electric power passes into other types.
Circuits where the conversion, transmission and receipt of electrical 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.
In order to calculate and study a direct current electric circuit (laboratory work usually serves for these purposes), an equivalent circuit is used, that is, an idealized circuit for calculating the real one. To get it, you need to replace all the elements of the circuit. Physical processes must be expressed in every mathematical description.
Resistive elements
A resistor is one of the electrical circuit receivers. It is characterized by active resistance, which is measured in Ohms. Resistive resistances or, as they are also called, active resistances are introduced into equivalent circuits in order to take into account the converted electromagnetic energy into other types.
The calculation of complex DC electric circuits is performed if you set the positive direction of all currents and voltages. Choose the direction of their node having a large potential to the node with lower potential.
With an independent resistance to current, the resistor is called linear, and the electric circuit is called linear resistive. The current-voltage characteristic is expressed through a linear function passing through the origin.
When analyzing such circuits, the principle of simplification is often applied, which consists in replacing complex sections of an electric circuit with simple ones. But the current and voltage should not change. Then the chain will fold to the simplest form. The connected resistive elements must be parallel and sequentially converted.
Serial and parallel connection
When connected in series 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 connected in parallel, a constant voltage is used, but the current is the sum of the currents on each of the elements. Therefore, it can be represented as the product of voltage and equivalent conductivity of active elements. And it, in turn, is equal to the sum of the conductivities of the elements. This is what direct current consists of.
DC electric circuits, in addition, contain voltage and current sources.
Sources
Independent voltage (EMF, current) from the resistance of an external circuit is called its source. The source of EMF (voltage) is measured at idle, that is, where the current in the source is zero. In equivalent circuits, the resistor takes into account thermal energy losses that are released from the source. If it is zero, and the current source is infinity, then this is an ideal source. Real always has final meaning.
External characteristics are as follows: for EMF and voltage sources, the dependence arises on the flowing current, and for the current source it depends on the voltage at the terminals.
Real sources have linear and non-linear sections. Consider methods for calculating linear DC electrical circuits. They are described in Ohm's law for a complete circuit, 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 non-linear DC electric circuits is based on the Kirchhoff law. The calculation methods for linear and nonlinear circuits are different. Therefore, the latter are not considered in the framework of this article.
Linear measuring instruments
The electrical capacitance of the DC circuit contains sources. And the instruments that measure it are: a voltmeter for measuring voltage in a section of the circuit and an ammeter for sequential inclusion in the circuit. With a zero value of internal resistance and conductivity, the devices are ideal.
Switching methods become more clear when considering them using a resistance measurement. According to Ohm's law, R = U / I.
We know that real devices do not have a zero value. Therefore, only two options for their inclusion are possible:
- the internal resistance of the voltmeter is several times greater than the measured ammeter - such that reducing the voltage on it does not reduce the decrease in the measured resistance, and the voltage measured by the voltmeter should correspond to the working range;
- the internal resistance of the voltmeter is commensurate with the measured, and the ammeter is significantly less than the measured.
Experiment and tasks for control work
To measure voltage and current, appropriate generators are used. Their internal resistance is measured by means of switches.
A voltmeter and an ammeter are included in unit AB1.
To measure the resistance, special schemes are used. In the source of electromotive force, the internal resistance must be off.
In the recommended task, which should have a control job, DC electric circuits are studied by determining the parameters of the electromotive force source, current source, resistance measurement, studying the inclusion of parallel and series resistance, CVC.