Studying the use of electric current, you need to be able to calculate the amount of electricity that is spent on a particular action - heating water in the kettle, lifting the elevator, etc. thereforelet's derive a formula for convenient calculation of current operation.
In the left parts of equalities there are different symbols, but they denote the same physical quantity - power. Therefore, the right sides of the formulas can be equated:I · U = A / t . Express work:
By this formula is calculatedcurrent work or, which is the sameconsumed electricity . We will clarify that these terms are synonyms.
When a source of electrical energy appears in the circuit, its electric field drives the charged particles inside the conductor (electrons and / or ions), and their energy increases. The sum of the energies of all particles of a body is the internal energy of the body (see § 7-e), which meansthe internal energy of the conductor at the time of its occurrence in it increases . According to the I law of thermodynamics (see§ 6-h), internal energy can be spent on heat transfer or performing mechanical work. But, being consumed, it is constantly replenished due to the energy of the current source.
The passage of current through the conductor - the work of the current - is always accompaniedcurrent actions (see § 8-з). At the same time, electricity is converted into other types of energy: heat (for example, iron, kettle), mechanical (for example, vacuum cleaner, fan) and so on. thereforeBy the term “current makes work” we will understand the transformation of electricity into other forms of energy. In this case, the work of the current and consumed electricity - expressions, synonyms.
To measure the electricity consumed are special measuring devices - electricity meters .
To account for the electricity consumed, instead of joule, a larger unit of work is used -kilowatt hour (designation: 1 kW · h). For example, the meter in the figure shows the value of 254.7 kW · h. This may mean, for example, that during the entire accounting period a consumer with a power of 254.7 kW worked for 1 hour or that a consumer with a power of 2547 watts worked for 100 hours (and so on, keeping the proportion).
Find the connection of thisunits of work with a more familiar unit for its measurement - the joule.
1 kWh = 1000 W · 60 min =
= 1000 J / s · 3600 s = 3 600 000 (J / s) · s =
= 3 600 000 J = 3.6 MJ
So, 1 kWh = 3.6 MJ.
FormulaA = I U t will help us figure out what the physical meaning of “electrical voltage” is. Express it from the formula.
This shows that 1 volt is a voltage at which a current of 1 ampere is capable of producing 1 joule of work in 1 second. In other words,voltage shows the work that the electric field forces do every second to maintain a current of 1 ampere in the current circuit.
In addition, from the formulaI = q / t (see § 9-b) it follows thatq = I · t. Then:
Based on this formula,1 volt can be considered as such a voltage at which the work of the forces of the electric field when moving along a charge conductor of 1 C will be equal to 1 J.
Based on the whole reasoning “below the line” we will say thatVoltage is one of the characteristics of the electric field moving charges along a conductor.
Electric current is generated in order to further use it for certain purposes, to perform any work. Thanks to electricity, all devices, devices and equipment are functioning.The work itself is a certain effort applied to move the electric charge for a set distance. Conventionally, such work within the chain section will be equal to the numerical value of the voltage at this section.
To perform the necessary calculations, it is necessary to know how the current is measured. All calculations are carried out on the basis of the initial data obtained using measuring instruments. The larger the charge, the more effort is required to move it, the more work will be done.
What is called current work
Electric current, as a physical quantity, does not in itself have a practical value. The most important factor is the action of the current, characterized by the work he does. The work itself is a definite action in which one kind of energy turns into another. For example, electrical energy, by rotating the motor shaft, is converted into mechanical energy. The work of the electric current itself consists in the movement of charges in a conductor under the action of an electric field. In fact, all work on the movement of charged particles is performed by an electric field.
In order to perform the calculations, the formula for the operation of the electric current should be derived. To compose the formulas will need parameters such as current strength and. Since the work of the electric current and the work of the electric field are one and the same, it will be expressed as the product of the voltage and the charge flowing in the conductor. That is: A = Uq. This formula was derived from the relation that determines the voltage in the conductor: U = A / q. It follows that the voltage is the work of the electric field A in the transfer of a charged particle q.
The charged particle itself or charge is displayed as a product of the current and time spent on the movement of this charge through a conductor: q = It. In this formula, the ratio for the current in the conductor was used: I = q / t. That is, it is the ratio of charge to the time it takes the charge to pass through the cross section of the conductor. In the final form, the formula for the operation of electric current will look like the product of known quantities: A = UIt.
In what units is the work of electric current measured
Before directly solving the issue of how the work of electric current is measured, it is necessary to collect the units of measurement of all physical quantities with which this parameter is calculated.Any work, therefore, the unit of measurement of this quantity will be 1 joule (1 j). Voltage is measured in volts, current intensity is in amperes, and time is measured in seconds. So the unit will look like this: 1 J = 1B x 1A x 1c.
Based on the received units of measurement, the operation of the electric current will be determined as the product of the current strength in the circuit section, the voltage at the ends of the section and the period of time over which current flows through the conductor.
Measurements are made using a voltmeter and a clock. These devices can effectively solve the problem, how to find the exact value of this parameter. When turning on the ammeter and voltmeter in the circuit, it is necessary to monitor their readings for a set period of time. The obtained data is inserted into the formula, after which the final result is displayed.
The functions of all three devices are combined in electric meters, taking into account the energy consumed, and in fact the work done by electric current. Here another unit is already used - 1 kW x h, which also means how much work was done during a unit of time.
Etc. For this purpose, electrical networks are laid in each apartment, the voltage of which is maintainedcurrent .
Can determinethe job current in proportion to his strength.So, the charge passes a section of the chain for a certain period of time equal to t. You can find its value by calculating the product of forcecurrent to this parameter: q = I t.
Substitute the resulting expression in the basic formula: A = U I t.
Unit of Workcurrent in the SI system is 1 Joule, named for the British physicist who derived the connection of thermal energy with mechanical work. 1 Joule is equivalent to a unit of energy created in a stationary electric field by force.current in 1 Amp, voltage 1 W for 1 second time.
There is also a so-called off-system unit of work.current which is expressed in kWh (kilowatt hour). It is used in the calculation of electricity in household and office premises and is indicated in the documents for the payment of utilities. 1 kWh is 3,600,000 Joules, or 3,600 kJ.
Electricity is the work of powercurrent , which takes place over a certain time interval and consumed by household appliances. In order for them to consume the minimum amount and, therefore, save the budget, it is necessary to pay attention to a different characteristic when buying.current - power.This value is equal tocurrent per unit of time.
Simplest transformercurrent (TT) consists of two copper windings, isolated from each other and wound on a steel core. Each of the windings has a certain number of turns, the ratio of which determines the transformation ratiocurrent . Errors that occur during the conversion of the primarycurrent in secondary, allow to carry TT to one of accuracy classes.
Currently there is a huge variety of TT. There are several classifications: by place of installation, by design, by type of insulation, etc. It will be difficult for an unprepared person in this area to immediately determine to which particular type this or that TT belongs. The easiest way to determine the type of TT is to decipher the symbol indicated on the plate attached to the TT itself (see Figure 1).
However, very often for some reason, there is no label with factory data on the body of the TT. In this case, you can use the factory documentation. Find a passport protocol for this type of equipment. The type of TT will be listed on its first page.In addition, the required information is often indicated in the circuit diagrams of this connection (circuit).
In the case when this method does not give the desired result, you can try to load this TT, that is, remove the current-voltage characteristic from it. This will require special equipment: progruzochnoy installation, clamp meter, volt-ampere-phase meter (VAF), alternating voltmetercurrent .
For a correct reading, it is necessary to apply current either to the terminals of the primary winding (a large current) and take valuescurrent and voltages from the secondary winding, or, conversely, to supply a small current to the terminals of the secondary winding of the CT, and from the primary to remove large valuescurrent and voltage. Then, using the data obtained, you will need to construct curves that determine the dependence of the voltages on the primary and secondary currents, as well as to determine the transformation ratiocurrent and the absolute error of the TT.
In appearance and the data obtained, using reference materials, you can approximately determine the type of the TT, its state (good / defective), as well as the accuracy class.However, in order to avoid mistakes, it is still better to contact a qualified specialist. It will not only save your time, but also give recommendations on the application, method of connection and maintenance of this device.
Very often there is a situation when it is necessary to adjust the work of a device. The master of the desired profile may not always be nearby, so you have to do the repairs yourself. But in order for the device to work, and you are not injured, you need to know what you are dealing with. That is, you need to determine the parameters of the current, and first of all -voltage .
You will need
- Voltmeter, multimeter, ammeter
Determine whether you are measuring constant or variablevoltage . Switch the meter or multimeter to DC or AC mode. Most often there is a need to measurevoltage power or electromotive force (EMF). Even if the approximate parameters of these voltages are unknown, then at the initial stage of measurement, the device should be switched to the maximum voltage measurement mode. Connect the device according to polarity.
This is an orderly movement of certain charged particles. In order to correctly use the full potential of electricity, it is necessary to clearly understand all the principles of construction and operation of electric current. So, let's see what is work and power current.
Where does electric current come from?
Despite the seeming simplicity of the question, few are able to give an intelligible answer to it. Of course, nowadays, when technologies are developing at an incredible speed, a person doesn’t particularly think about such elementary things as the principle of the electric current. Where does electricity come from? Surely many will answer "Well, from the outlet, of course," or just shrug their shoulders. Meanwhile, it is very important to understand how the current works. This should be known not only to scientists, but also to people who are not connected in any way with the world of sciences, for their universal, diversified development. But to be able to correctly use the principle of operation of the current is not for everyone.
So, for a start it should be understood that electricity does not arise from anywhere: it is produced by special generators, which are located at various power plants.Due to the rotation of the turbine blades with steam, obtained by heating water with coal or oil, energy is generated, which is subsequently converted into electricity by means of a generator. The generator is very simple: in the center of the device there is a huge and very strong magnet, which causes electric charges to move along the copper wires.
How does electric current reach our homes?
Once a certain amount of electric current has been received with the help of energy (thermal or nuclear), it can be supplied to people. Such a supply of electricity works as follows: in order for electricity to reach all apartments and enterprises successfully, it must be “pushed”. And for this you need to increase the force, which will do it. It is called the electrical voltage. The principle of operation is as follows: the current passes through a transformer, which increases its voltage. Further, the electric current goes through cables installed deep underground or at a height (for sometimes the voltage reaches 10,000 volts, which is deadly to humans).When the current reaches its destination, it must again pass through a transformer, which now reduces its voltage. It then runs along wires to installed shields in apartment buildings or other buildings.
The electricity carried through the wires can be used through a system of sockets, connecting household appliances to them. In the walls, however, additional wires are carried through which electric current flows, and it is thanks to him that the lighting and all the appliances in the house work.
What is current work?
The energy that carries an electric current, over time is converted into light or heat. For example, when we turn on a lamp, the electrical form of energy turns into light.
Speaking in accessible language, current work is the action that electricity itself produced. At the same time it can be very easily calculated by the formula. On the basis of the law on the conservation of energy, we can conclude that electrical energy is not lost, it has completely or partially changed to another form, while giving a certain amount of heat. This heat is the work of the current when it passes through a conductor and heats it (heat exchange occurs).This is what the Joule-Lenz formula looks like: A = Q = U * I * t (the work is equal to the amount of heat or the product of the power of the current by the time during which it flows through the conductor).
What does direct current mean?
Electric current is of two types: AC and DC. They differ in that the latter does not change its direction, it has two clips (positive "+" and negative "-") and always starts its movement from "+". And alternating current has two terminals - phase and zero. It is because of the presence of one phase at the end of the conductor, it is also called single phase.
The principles of a single-phase alternating and direct electric current are completely different: in contrast to a constant, an alternating one changes its direction (forming a flow both from the phase towards zero and from zero towards the phase) and its value. For example, alternating current periodically changes the value of its charge. It turns out that at a frequency of 50 Hz (50 oscillations per second) the electrons change the direction of their movement exactly 100 times.
Where is DC current used?
Constant electric current has some features. Due to the fact that it flows strictly in one direction, it is more difficult to transform. Sources of direct current can be considered the following elements:
- batteries (both alkaline and acid);
- conventional batteries used in small devices;
- and also various devices like converters.
What are its main characteristics? This is the work and power of the current, both of which are very closely related to each other. Power implies a speed of work per unit of time (for 1 s). According to the Joule-Lenz law, we find that the work of a direct electric current is equal to the product of the strength of the current itself, the voltage, and the time during which the work of the electric field was performed in charge transfer along a conductor.
This is the formula for finding the current operation with consideration of Ohm’s resistance law in conductors: A = I 2 * R * t (work is equal to the square of the current strength multiplied by the value of the conductor resistance and again multiplied by the time it took to work)