Electrical circuit - a set of dissimilar elements connected by conductors, designed for current flow. The range of components is wide. Elements produce linear, nonlinear, active, passive. The classification is powerless to cover possible cases.
The composition of the electrical circuit
The electrical circuit includes( in general): a power source, a switch( switch), connecting wires, consumers. Be sure to form a closed loop. Otherwise, no current can flow through the circuit. Electric is not called the contours of the ground, grounding. However, in fact, are considered as such, sometimes a current flows here. The circuit closure during grounding, zeroing is ensured by means of soil.
Power Supplies. Internal, external electrical circuit
For the formation of an orderly movement of charge carriers, forming a current, take the trouble to create a potential difference at the ends of the plot. Achieved by connecting the power source, which in physics is called the internal electrical circuit. In contrast to the other elements that make up the external. At the power supply, the charges move against the direction of the field. Achieved by the application of third-party forces:
- Generator winding.
- Galvanic power supply( battery).
- Transformer Output.
The voltage generated at the ends of a section of an electrical circuit is variable, constant. According to the technique, it is customary to divide the contours accordingly. The electrical circuit is designed for the flow of direct, alternating current. Simplified understanding, the law of change in the orderly movement of charge carriers is perceived as complex. It is difficult to understand whether the alternating current in the circuit is constant or constant.
In addition to the orderly movement, carriers are characterized by chaotic thermal motion. Speed (intensity) is determined by temperature, type of material, some other factors. In the formation of an electric current, the type of motion does not actually take part.
The type of current is determined by the source, the nature of the external electrical circuit. The galvanic cell gives a constant voltage, the windings( transformers, generators) - variable. Associated with the processes occurring in the power source.
Third-party forces that provide the movement of charges, called electromotive. Numerically, EMF is characterized by the work done by the generator to move a unit charge. Measured in volts. In practice, for calculating circuits, it is convenient to divide power sources into two classes:
- Voltage sources( EMF).
- Current sources.
In reality, unknown, trying to create an imitation of practice. In the outlet we expect to see 230 volts( 220 volts according to old standards).Moreover, GOST 13109 uniquely establishes the limits of deviation of parameters from the norm. In everyday life we use a voltage source. The parameter is normalized. The magnitude of the current does not matter. Voltage substations day and night seek to make permanent, regardless of the current consumer request.
In contrast, the current source supports a given law of the orderly movement of charge carriers. The voltage value does not matter. A striking example of this kind of device is a welding machine based on an inverter. Everyone knows: the diameter of the electrode is strongly associated with the thickness of the metal, other factors. In order for the welding process to proceed correctly, it is necessary to maintain current with a high degree of constancy. The task is solved by an electronic unit based on an inverter.
Current, voltage are constant, variable. The law of change of the parameter does not matter. It does not matter if the electrical circuit is connected to a constant, alternating voltage source. However, it is important to sustain the correct parameter size. For example, the effective value of the EMF.
A switch will allow you to connect the power source to the wires, the consumer. Everyone( with rare exceptions) used a wall switch. When the circuit-disconnection of an electric circuit occurs a spark. Explained by the presence of capacitive resistance type. To prevent sparking, the circuit is supplemented with a choke, the switch is formed by contactors of a special type. Other technical solutions are invented, for example, Tesla coil.
In the technique of the wire is made of copper, aluminum. Associated with low resistivity of metals. The price is low. The heat released on the conductors is determined by two parameters:
- The resistance of the chain section.
- Electrical Current.
Clearly, the second parameter is determined by the needs of consumers. Supplier seeks to influence first. Conductor resistivity is foreseen as low as possible. Scientists have long been interested in the phenomenon of superconductivity. Metals lose resistance when temperature decreases. Reduced losses. Among semiconductors there are samples with positive and negative temperature coefficient of resistance. The absolute value of the metal parameter is orders of magnitude lower.
The problem with aluminum, copper is simple: when an electric current flows in the circuit, the temperature rises. The resistance of the plot increases, further aggravating the situation. It turns out a vicious circle. Scientists believe that it is permissible to correct the difficulty by enlisting the effects of superconductivity.
Metal at a certain low temperature dramatically, with a jerk reduces the resistance, reaching zero( above the boundary, the graph goes down smoothly at a speed of 1/273 1 / deg).The problem of practical application is that the values that provoke a jump are low. For example, for lead, the threshold is 7.2 K. Extremely low negative temperature on the Celsius scale.
Scientists see a solution to the problem of discovering materials that demonstrate the phenomenon of superconductivity at room temperature. Then it will be possible to transfer large currents to consumers, avoiding losses. In an electrical circuit formed by superconductors, charges are able to circulate for an infinitely long time without external feed source.
A new phenomenon discovered Heike Kamerlingh Onnes in 1911, examining samples of mercury cooled to very low temperatures. At four degrees Kelvin, the wire resistance became zero, before the jump decreased, smoothly following a straight line. It became clear: a new material condition was discovered. Later, the phenomenon of superconductivity was demonstrated on samples of other metals. It is shown: the effect is destroyed by placing the experimental substance in a strong magnetic field. Technetium boasts the highest threshold temperature among metals( 11.3 K).
For artificial materials, indicators are much higher. Since 1986, scientists have been exploring a variety of ceramics. We consider the last confirmed fact to be information on the availability of composite materials based on mercury oxides with a transition temperature to a new state at the 140 K boundary. Further work is classified for obvious reasons.
Consumer of an electrical circuit is understood as not related to the elements listed above. The useful load is an ordinary incandescent bulb, a heater coil, an electric motor. The parameters of the chain are very dependent on consumers. For example, the windings of transformers are endowed with strongly pronounced inductive resistance. Negatively affects the transfer of energy from the source.
Not only the current changes direction. Sometimes the statement concerns power. Energy begins to circulate here and there, heading for the power source, back to the external circuit. Reactive power is powerless to do useful work, warms the conductors of the circuit, distorts the shape of the useful signal. Manufacturers accounting for total consumption are encouraged to include compensating capacitors in parallel with the engines. Inductive resistance is compensated by capacitive, reactive power is closed inside the consumer segment, avoiding to go outside, not emitting too much heat on the network cables.
It should be noted an important property of inductive consumers: consume energy. The electric current becomes a magnetic field, transmitted further. In motors, the oscillations of the vector of tension generated by the winding will allow the shaft to perform useful work. In order to show the energy waste that is occurring, the circuits supplement the sources of electromotive force( current), the direction of which is opposite to being in the internal electrical circuit.
Power transmission through capacitive coupling is not invented today. However, approximately we consider as a similar case the radiation of a radio wave to the ether. The simplest Hertz vibrator is often represented by an oscillating circuit, in which the capacitor plates are separated to the sides. The step will allow the formation of an electromagnetic wave carried by the ether. As for the transfer of high power, Nikola Tesla built the corresponding plans; everyone saw the Vordenklif tower in the photo, a stylistic image, which resembles a boletus with a straight leg. With the help of a network of buildings, it was supposed to power industry, factories and plants by wireless communication.
In the course of electronics receivers are mainly considered. Between the antenna terminals, wave transmission over the air is indicated schematically by a source of alternating voltage of low power. The captured emf is amplified by cascades including resonant circuits. Electronics, like no other field of technology, includes an incredible variety of consumers. Simplifiedly divided into two classes:
- Active consumers require the supply of electrical energy for proper operation. As a rule, can not eat directly the main network. Chips, discrete active elements: transistors, thyristors. In other words, electronic keys. Electric motors are fundamentally different, powered by the input network.
- Passive consumers do not require external power. However, the current can flow in a fancy way. Some thyristors open when the voltage reaches a certain value. Therefore, they are considered to be passive devices, have a non-linear characteristic. Diodes passing a current in one direction belong to this family( they demonstrate valve properties).
Passive consumers are all kinds of resistors, capacitors, chokes( inductors).With the help of elements, an electrical circuit acquires unusual qualities. Resonant circuits of capacitors, inductances are used by filters of waves of various frequencies.