Talks on Electrical Engineering: Electricity - from simple to complex. Part 3.
Interestingly, even in strong electric fields the average velocity increment is not more than a few centimeters per second. And at the same time it provides the electrical field is incremented each of the free electrons in a circuit almost simultaneously. This is called the velocity of propagation of the electric field in a conductor. It is a value slightly greater than 200,000 km per second! Slightly less velocity of light in vacuum (300,000 km per second).
Any source or electric field generator is characterized by an electromotive force (EMF), which is generated by the electric field is reported to navigate through the electronic circuit. EMF is measured in volts. When you move the electric charge in one coulomb (1 C) a current source for the work in one joule (1 J), if the source has an EMF of 1 V. If the EMF is, for example, 5 V, then the work carried out corresponds to 5 Dzh. Incidentally, 1 J - is working on lifting cargo weighing 109 g to a height of 1 m!
Thus, the current source due to certain internal processes to external output allows some difference in the electrical states, or EMF. But when we connect some - or conduction system, these electrodes in this system begins to flow electric current. Here is the external, electrically conductive system is called an electrical circuit! And due to the fact that this circuit is (by definition), both electrodes EMF source, such external circuit is closed. In the most general case, the external electric circuit is characterized by a parameter such as resistance (R), which is expressed by the following relationship:
It is useful to remember: 1 mV = 1000 mV = 1000000. 1 A = 1000 mA = 1000000 uA. 1 ohm = 0.001 k = 0.000001 MW. Or, more familiar: 1M ohms = 1000 = 1,000,000 ohms. In general, we say that the circuit through which the current flows of 1 A at a voltage of 1 V, has a resistance of 1 ohm.
The electronics are often used and such values are 1 mA = 1000 = 1000000 pA. 1 GOhm = 1000 MW = 1,000,000 ohms = 1000000000 Om! 1 kW = 1000 V. In order to easily and clearly describe the operation of arbitrarily complex electrical circuits, adopted a system of symbols. We use them to represent two simple circuits. Figure 5, and shows the electrical circuit of an ordinary portable flashlight.
It contains a light bulb A, the switch S and the EMF source (battery) G. As the batteries can be used, "Kron" or BSC. The image of any electrical circuit (documentation) using a system of conditional graphic designations of elements, is the standard name of a circuit diagram of this circuit.
Thus, 5b is a schematic diagram of a circuit comprising a resistor R1, and the battery switch S G. Generally, a resistor in the electrical and electronics especially finds broadest application. Getting to know some of the properties of the resistor will begin with Ohm's law. If close the switch S, the current flow is ensured I, which is easily determined from the relationship in the simplest circuit: I = U / R, where U - source voltage, V; R - electrical resistance, Ohm.
Electrical resistance is a value inversely proportional to the conductivity. Of course, if you make this resistance of a material lattice which has a complex structure, such as the distance between the lattice sites are small, then the increment of average velocity of the electrons when an electric field is small!
This happens due to the fact that the rate of surplus absorbed by the crystal structure in collisions of free electrons with the lattice atoms. The atoms get additional energy, which has a thermal character. Therefore, it is reasonable to say that the resistors are transformed energy of the electric field, ie, energy source - to heat.
The thermal energy (Figure 6, a) is easy to calculate by the formula
This means that the load (in this case a resistor R) consumes electrical energy from the power equal to P. Note that the potential difference at the points "A" and "B", as is easily seen from Figure 6, and is U. This case we say that a drop between points "A" and "B" is equal to U. We now turn to Figure 6, b. wherein the two resistors, namely, R1 and R2 are included in series with respect to the voltage source. In this case: I = U / (R1 + R2); U = I (R1 + R2). But the voltage drop across the resistors R1 and R2 can be written as
Consider another case. Figure 7 shows the so-called mixed connection of resistors R1, R2 and R3, ie, Series resistor R1 and R2 groups and resistors R3, connected together in parallel.
For this case, we can write
But what is enough visual electronic circuits can be assembled virtually, on the basis of already achieved "theoretical level"? Currently, one of the most common and cheap electronic components are so-called LEDs.
This amazing product! According to its name, they are able to emit light. So they are some kind of light bulb? And here and there, because the physical mechanism of the LED light is quite different. For comparison - the incandescent filament bulbs, which is used in flashlights, red-hot almost to 2000 ° C! A crystal of the LED is almost cold, because the temperature rarely exceeds 50 ° C. In addition, the lamp emits a whitish yellow light, and the LED only choose - spectrally pure colors: yellow, green, orange, red! In recent years, there were even blue and blue.
Comments
Commenting, keep in mind that the content and the tone of your messages can hurt the feelings of real people, show respect and tolerance to his interlocutors, even if you do not share their opinion, your behavior in terms of freedom of speech and anonymity offered by the Internet, is changing not only virtual, but real world. All comments are hidden from the index, spam control.