If this value is smaller, it will decrease by a factor of resistance conductor.
If possible, reduce the length of the conductor that is used in the chain. The resistance is directly proportional to the length of the conductor. If we shorten the conductor by n times, then resistance it will go down by the same amount.
Increase the cross-sectional area of the conductor. Install a conductor with a large cross-section or connect several conductors in parallel into a bundle of wires. How many times the cross-sectional area of the conductor will increase, it will decrease by as much resistance conductor.
You can combine these methods. For example, to lower resistance conductor in 16 times, we replace it with a conductor, specific resistance 2 times less, we reduce its length by 2 times, and the cross-sectional area by 4 times.
To decrease resistance location on chain, connect to it in parallel one more resistance, the value of which is calculated. Please note that with parallel connection, resistance The chain segment is always smaller than the small resistance, located in parallel branches. Calculate the necessary resistance, which must be connected in parallel. For this, measure resistance of the R1 chain. Identify that resistance, which should be on it - R. Then determine resistance R2, which must be connected to the resistance R1 in parallel. To do this, find the product resistances R and R1 and divide by the difference of R1 and R (R2 = R1 / (R1-R)). Note that by condition, R1 is always greater than R.
Resistance is a certain ability of an element of an electric chain to prevent passage of an electric current through it. They have various materials, for example, copper, iron and nichrome. The total resistance is the resistance of the entire electrical circuit as a whole. It is measured in Ohms. It is necessary to know the resistance of the circuit for evaluating the short-circuit currents and the selection of switching devices.
You will need
- Ohmmeter, measuring bridge, calculator.
Instructions
First, determine how to connect the elements electric circuit in relation to each other, since this affects the calculation of the total resistance. Conductors can be in serial or parallel connection. Serial connection - this is connection, when all the elements are connected so that the part of the chain that includes them has no nodes, and the parallel connection is is connection, when all the elements of the circuit are united by two nodes and not have a links with other nodes.
If you have determined that the conductors in the electrical circuit are connected in series, it is not difficult to find the full resistance. Just add up the resistance of all elements . If you are not given the resistance of each conductor, but given their voltage and current strength of any element of the circuit, then, having combined all the voltages, you will recognize the total voltage. The current strength of each element in a series connection is equal, that is, total the current strength in the entire circuit is equal to the current strength of any conductor given conversations . And then, to find the impedance, divide the total voltage by the current.
If the elements are connected in parallel, the total resistance can be found in the following way: multiply the resistance of all conductors and divide by their sum. If you are not given the resistance of each element, but given their current strengths and tension any element of the chain, then, having combined all the strength of the current, you will know the common. The voltages of each element in parallel connection are equal, that is, the total voltage in the entire circuit is equal to the voltage of any conductor of a given chain. And then, in order to find the impedance, divide the voltage by the total current.
To determine the total resistance of an electrical circuit, use such measuring devices , like an ohmmeter and a measuring bridge. They will help you determine the electrical resistances.
Helpful advice
Be sure to determine how to connect the elements in the electrical circuit, since it depends on it depends on the correct calculation of the total resistance!
Sources:
- calculate the resistance of the circuit in 2017
Resistance wires shows how much it prevents the passage of an electric current. Measure it with a tester switched to the ohmmeter mode. If this is not possible, you can calculate it in many ways.
You will need
- - Tester;
- - ruler or tape measure;
- - calculator.
Instructions
Measure the resistance wires. To do this, connect the tester connected to the ohmmeter mode to its ends. The device will display electrical resistance wires in Ohms or fold the values, depending on the settings of the device. The wire must be disconnected from the power source.
Calculate the resistance using a tester that working in the mode of ammeter and voltmeter. If the wire is an connect it to a power source. To the ends wires In parallel, connect the tester included in the operating mode of the voltmeter. Measure the fall stresses on the wire in volts.
Switch the tester to the operating mode of the ammeter and turn it on in a circuit in series. Get the current value in the circuit in amperes. Using the ratio obtained from Ohm's law, find the electrical resistance of the conductor. To do this, divide the value of the voltage U by the current I, R = U / I.
Example. The measurement showed that when the voltage on the conductor is 24 V, the current in it is 1.2 A. Determine its resistance. Find the ratio of voltage to current strength R = 24 / 1,2 = 20 Ohm.
Find Resistance wires, without connecting it to the power source. Find out what material made the wire. In the specialized table, find the resistivity of this material in Ohm ∙ mm2 / m.
Calculate the cross-section wires, if it is not specified initially. To do this, clean it of insulation, if it is insulated, and measure the diameter of the conductor in mm. Determine its radius by dividing the diameter by the number 2. Determine the cross section wires, multiplying the number π≈3,14 by square of the radius veins.
Using a ruler or a tape measure the length wires at meters away . Calculate resistance wires, multiplying the resistivity of the material ρ by the length of the conductor l. Divide the result by its section S, R = ρ ∙ l / S.
Example. Find the resistance of copper wires with a diameter of 0.4 mm and a length of 100 m. The resistivity of copper is 0.0175 Ohm ∙ mm2 / m. Radius wires is 0.4 / 2 = 0.2 mm. Section S = 3.14 ∙ 0.2² = 0.1256 mm². Calculate the resistance according to the formula R = 0,0175 ∙ 100 / 0,1256≈14 Ohm.
Sources:
- copper conductor resistance
If the electrical circuit is closed, creating a potential difference at its ends, then an electric current will run along it, the strength of which can be measured by an ammeter. But this force will vary if in the circuit one conductor is replaced by another. This suggests that not only does the voltage affect the current, but also the material from which the conductor is made. This property of the conductor prevents the passage of an electric current and is called resistance.
Each body in relation to the electric current is characterized by its resistance. If we recall the electronic theory, then according to it, all substances consist of atoms and molecules. These atoms and molecules in different substances have different structures. And it is they that are found on the path of free electrons in the conductor, when a current flows through the electrical circuit. That is, when a free electron collides with an ion of the crystal lattice of a conductor material, it inevitably loses some of its kinetic energy and experiences, as it were, resistance to its movement.
The greater the resistance of the conductor, the less it passes the electric current. The electrical resistance is denoted by the Latin letter R, and 1 ohm is taken as the unit of measurement.
The inverse characteristic of the resistance of a substance is its conductivity. The higher the electrical conductivity of the material, the better it conducts the current. Insulators differ from conductors by conductivity in an enormous number of times, measured by a unit with twenty-two zeros!
Resistivity. Definition and calculation
So, the electrical resistance depends on the material from which the conductor is made. But there are two more important parameters - the length of the conductor and the area of its cross section. Obviously, the longer the conductor, the longer the ions of its substance will interfere with the motion of free electrons.
But to better understand why the resistance depends on the cross-sectional area, you need to draw an analogy with water. Imagine two identical vessels, connected in one case by a thin tube, and in the other - thick. On a thin or thick tube, the water will quickly pour from one vessel to another? Clearly, on a thick.
The resistivity is the conductor resistance, 1 meter long and 1 mm2 cross-sectional area.
The least resistivity is silver and copper.
Thus, in order to calculate the electrical resistance of a conductor, we must use the formula:
R = pl / S,
where p is the resistivity, l is the length of the conductor, S is the cross-sectional area of the conductor.
When the temperature of the metallic conductor rises, its resistance increases. This phenomenon can be explained by the fact that when the heat energy is transferred to the body, the intensity of the motion of the atoms of its substance increases, and this largely hinders the free current of the electrons.
With the lowering of the temperature in metals, better conditions are created for conducting an electric current. There is even is a concept like superconductivity, that is, a state of a metallic conductor when its resistance is zero. In this case, the metal atoms practically freeze in place, absolutely not interfering with the motion of free electrons. This occurs at a temperature of -273 ° C.
Sources:
- School for an electrician
When calculating the cross-section of a cable, in private housing construction or in apartments to determine this value, two indicators are used: the power consumption of the network and the current that passes through the wiring. Resistance in this case does not play a role. It's all about the small length of the wires. But if the length of the power transmission line is sufficiently large, then it is impossible to do without determining this indicator. For example, at the beginning of the section, the voltage will be 220-2240 volts, and at the end it is already underestimated 200-220 volts. And as copper cables and wires are increasingly used in wiring, our task in this article is to consider the resistance of a copper wire (the resistance table of wires will be lower attached).
What does resistance give us in general? In principle, with its help you can find out the parameters of the wire used or the material from which it is made. For example, if a hidden method was used to lay the transmission line, then knowing the resistance of the line, it is possible to say exactly how long it is. After all, the gasket is often made underground and indirectly. Or one more option, knowing the length of the section and its resistance, you can calculate the diameter of the cable used, and through it and its cross section. Plus, knowing this value, you can find out the material from which this wire was made. This all suggests that you should not discount this indicator.
All this concerned electrical wiring, but when it comes to electronics, in this area, without determining resistance and comparing it with other parameters is indispensable. In some cases, this parameter can play a decisive role, even an improper selection of the resistance wire can lead to the fact that the device connected to such a conductor simply will not work. For example, if you connect a very thin wire to the power supply of a standard computer. The voltage in such a conductor will become low, not much, but it will suffice to make the computer work incorrectly.
What determines the resistance
Since we are talking about copper wire, the first on which this physical parameter depends is copper, that is, raw material. The second is the dimensions of the conductor, or, more precisely, its diameter or cross-section (both quantities are related by a formula).
Of course, there are additional physical quantities that affect the resistance of the conductor. For example, the ambient temperature. After all, it is known that when the temperature of the wire increases, its resistance increases. And since this indicator is inversely related to the strength (density) of the current, the current, respectively, when the resistance is increased, decreases, on the contrary. True, this applies to metals that have a positive temperature coefficient. For example, a tungsten alloy, which is used for the filament of a light bulb, can be cited. Such material changes in the strength (density) of the current are not terrible at high heating, because this metal has a negative temperature coefficient.
Calculation of resistance
Today, everything is done for man. And even such a simple calculation can be done in several ways. There are simple, there are complex. Let's start with simple ones.
The first option is tabular. What is its simplicity? For example, the table in the lower figure.
Here everything is clearly shown and interconnected. Knowing the specific dimensions of the copper wire, you can determine its resistance and the amount of current that the wire can withstand. Or, conversely, having resistance or strength (current density) indicators, which, by the way, can be determined by a multimeter, it is easy to determine the cross-section or the diameter of the conductor. This option is the most convenient, tables can be found in free access on the Internet.
The second way to determine - using a calculator (online). Such Internet devices are great, working with them is convenient and easy. You can insert physical quantities of a copper conductor into such a calculator and get dimensional indicators, or, conversely. True, the bulk of such calculators in its program has one standard value - this is the resistivity of copper, equal to 0.0172 Ω · mm² / m.
And the most difficult variant of calculation is to conduct it yourself, using the formula. Here it is: R = pl / S, where:
- p is the same resistivity of copper;
- l is the length of the copper wire;
- S is its section.
I would like to note that copper has one of the lowest resistivities. Below it only silver - 0.016.
Determine the cross-section of the conductor through the formula, where the main parameter is its diameter. But to determine the diameter can be in different ways, by the way, such an article on our site is, you can read and get full and reliable information.
Content:When designing electrical networks in apartments or private houses, the calculation of the cross-section of wires and cables is compulsory. To carry out the calculations, indicators such as the value of the power consumption and the current that will pass through the network are used. Resistance is not taken into account because of the short extension of the cable lines. However, this indicator is necessary for long transmission lines and voltage drops in different sections. The resistance of the copper wire is of particular importance. Such wires are increasingly used in modern networks, so their physical properties must be taken into account in the design.
Concepts and meaning of resistance
The electrical resistance of materials is widely used and accounted for in electrical engineering. This value allows you to establish the basic parameters of wires and cables, especially with a hidden way of laying them. First of all, the exact length of the laid line and the material used to produce the wire are set. Calculating the initial data, it is quite possible to measure the cable.
Compared to conventional electrical wiring, in electronics, the resistance parameters are given decisive importance. It is considered and compared in conjunction with other indicators that are present in electronic circuits. In these cases, the incorrectly selected resistance of the wire, can cause a malfunction in the operation of all elements of the system. This can happen if you use too thin a cable to connect to the computer power supply. There will be a slight decrease in voltage in the conductor, which will cause the computer to work incorrectly.
Resistance in a copper wire depends on many factors, and first of all on physical properties of the material itself. In addition, the diameter or section of the conductor, determined by the formula or a special table, is taken into account.
Table
The resistance of the copper conductor is affected by several additional physical quantities. First of all, the ambient temperature must be taken into account. Everyone knows that when the temperature of the conductor rises, there is an increase in its resistance. Simultaneously, the current decreases due to the inverse proportionality of both quantities. First of all, this applies to metals with a positive temperature coefficient. An example of a negative coefficient is a tungsten alloy used in incandescent lamps. In this alloy the current does not decrease even at very high heating.
How to calculate resistance
There are several ways to calculate the resistance of a copper wire. The simplest is the tabular version, which shows the interrelated parameters. Therefore, in addition to resistance, the current strength, diameter or cross-section of the wire is determined.
In the second case, a variety is used. In each of them a set of physical quantities of copper wire is inserted, with the help of which the exact results are obtained. Most similar calculators use copper resistance of 0.0172 ohm * mm 2 / m. In some cases, such an average value may affect the accuracy of the calculations.
The most difficult option is hand calculations, using the formula: R = p x L / S, where p is the resistivity of copper, L is the length of the conductor, and S is the cross-section of this conductor. It should be noted that the resistance of the copper wire table determines how one of the lowest. The lower value is possessed only by silver.