As soon as we start studying physics in the school curriculum, almost immediately teachers begin to tell us that there is a very big difference between current and voltage, and we will need its knowledge in later life. And yet, now even an adult can often not tell about the differences between the two concepts. But everyone needs to know this difference, because we deal with current and voltage in everyday life, for example, turning on a TV or a phone charger into a power outlet.

Definition

current The process is called when, under the influence of an electric field, the ordered movement of charged particles begins. Particles can be a variety of elements, it all depends on the specific case. If we are talking about conductors, then the particles in this situation are electrons. Studying electricity, people began to understand that the possibilities of current make it possible to use it in various fields, including medicine. After all, electric charges help resuscitate patients, restore heart function. In addition, current is used in the treatment of complex diseases such as epilepsy or Parkinson's disease. In everyday life, it is simply irreplaceable, because with its help light is on in our apartments and houses, electrical appliances work.

Voltage- the concept is much more complex than current. Single positive charges move from different points: from a low potential to a high one. And voltage is the energy expended on this movement. For ease of understanding, an example is often given with the flow of water between two banks: current is the flow of water itself, and voltage shows the difference in levels in two banks. Accordingly, the flow will be until the levels are equal.

difference

Probably, the main difference between current and voltage could already be seen from the definition. But for convenience, we will give two main differences between the concepts under consideration with a more detailed description:

1. Current is the amount of electricity, while voltage is a measure of potential energy. In other words, both of these concepts are highly dependent on each other, but at the same time they are very different. I (current) = U (voltage) / R (resistance). This is the main formula by which you can calculate the dependence of current on voltage. Resistance is influenced by a number of factors, including the material from which the conductor is made, temperature, and environmental conditions.
2. The difference is in receiving. The impact on electrical charges in different devices (for example, batteries or generators) creates a voltage. And the current is obtained by applying a voltage between the points of the circuit.

The inability to see electrical current and the flow of charges with one's own eyes has always been a problem for those trying to grasp basic electrical concepts. The two main components of research, current and voltage, are generally misunderstood by those trying to understand the topic. This article will help you understand the difference between them.

The basic concepts of electricity revolve around one atomic component, the electron. Unstable atoms have either a deficit or extra electrons in their valence band. Extra electrons from one unstable atom tend to the valence band of an atom with an electron deficit.

With the help of an external electrochemical source, it is possible to create the movement of electrons. Any two terminals can be used to connect this charge source and create two contacts one positive and one negative.

The potential difference between two such points, one of which acts as a source and the other as a receiver of electrons, is called voltage. The unit of voltage is the volt, and its symbol is " V".

The flow of electrons in a conductor causes a current. The direction of the current goes from the positive pole to the negative. But electric charges, i.e. electrons, actually travel from the negative to the positive potential of the source. The amount of electric charge flowing through a unit cross-sectional area of ​​a conductor is called current strength. The current strength is measured in amperes, and has the symbol " I".

Circuit breakers

The fuse is used in electrical circuit and electrical work to interrupt the flow of excessive current through its components. Manufacturers of electrical fuses indicate characteristics using two parameters - voltage and current. The fuse selection criteria depend on the rated voltage of the circuit in which it will operate.

The current characteristics of the fuse do not depend on the type of current flowing through it - AC or DC. It depends only on the magnitude of the current at the moment of melting the fusible wire. Although the thickness of the wire and the type of metal wire used is a factor directly related to the current performance of the equipment. This is because the heat generated by the fusible wire is a function of the square of the current flowing through the conductor multiplied by the resistance and the current flow time.

The effect of batteries on current and voltage

Accumulators (batteries) are generally rated by the amount of current (amps) they can supply continuously for one hour. Therefore, the characteristics of the batteries are indicated in ampere-hours. Battery life depends on the load connected through it. Heavy loads tend to shorten battery life, while light loads increase battery life.

If the batteries are connected in series combination in an electrical circuit, the power supply network, the voltage in the circuit will increase, and the current in the circuit will remain at the same level.

Parallel connection of voltage sources is used to increase the current without increasing the voltage.

Water flow analogy

Consider two tanks connected by a transparent tube, the water in them is kept at the same height from the ground. There is no water flow in the tube.

Now, if we change the position of one of the tanks to create a potential difference, we will notice that water flows through the tube from a container with a higher potential to a container with a lower potential. Instead of changing water levels, we can also use water pumps for the same purpose. Valves can be used to control the amount of water flowing in a pipe from one reservoir to another.

An analogy can be drawn between this situation and a simple electrical circuit. The water pump is used to pressurize the water in the stream, let's call it "voltage". Water behaves like charged electrons. The flow of water is analogous to the movement of electrons, and the amount of water flowing through a unit cross-sectional area of ​​a pipe is analogous to "current". The higher potential reservoir is the "power source" and the amount of water it contains is the "accumulator capacity". Any crane installed along the pipe can be considered as a "load". electric installation work

Stupid question, you say? Not at all. Experience has shown that not too many people can answer it correctly. The language also introduces a certain confusion: in the expression “a 12 V source is available for sale”, the meaning is distorted. In fact, in this case, we mean, of course, a voltage source, not a current source, since the current is not measured in volts, but it’s not customary to say so. The most correct thing to say is “12 volt DC power supply”, but you can also write “power supply \u003d 12V” where the “=” symbol indicates that this is DC voltage, not AC. However, in this book we will also sometimes "make mistakes" - language is language.

To understand all this, first we recall the strict definitions from the textbook (memorizing them is a very useful exercise!). So, the current, more precisely, its magnitude, is the amount of electric charge flowing through the conductor cross section per unit time: / = Qlt. The unit of current is called "ampere", and its dimension in the SI system is coulombs per second, knowledge of this fact will be useful to us later.

The definition of voltage looks much more confusing - the magnitude of voltage is the difference in electrical potentials between two points in space. It is measured in volts, and the dimension of this unit of measurement is joule per pendant, that is, U - EIQ. Why this is so is easy to understand, having delved into the meaning of the strict definition of the magnitude of voltage: 1 volt is such a potential difference at which the movement of a charge of 1 coulomb requires an expenditure of energy equal to 1 joule.

All this can be clearly imagined by comparing the conductor with a pipe through which water flows. With such a comparison, the current can be imagined as the amount (flow) of water flowing per second (this is a fairly accurate analogy), and the voltage can be imagined as the pressure difference at the inlet and outlet of the pipe. Most often, the pipe ends with an open valve, so that the outlet pressure is equal to atmospheric pressure, and can be taken as zero. Similarly, in electrical circuits, there is a common wire (or "common bus" - colloquially for brevity it is often called "ground", although this is not accurate - we will return to this issue later), the potential of which is taken as zero and relative to which all voltages in the circuit are read out. Usually (but not always!) The negative terminal of the main power supply of the circuit is taken as a common wire.

So, back to the question posed in the title: so what is the difference between current and voltage? The correct answer will sound like this: current is the amount of electricity, and voltage is a measure of its potential energy. An interlocutor inexperienced in physics, of course, will begin to shake his head, trying to understand, and then such an explanation can be given. Imagine a falling stone. If it is small (the amount of electricity is small), but falls from a great height (high voltage), then it can cause as much misfortune as a large stone (a lot of electricity), but falling from a low height (low voltage).

The question may seem silly at first glance. Experience has shown that not many people can answer it correctly. The language introduces a certain confusion: in an expression like this - "there is a 6 volt direct current source on sale" the meaning is distorted. In fact, in this case, of course, a voltage source is assumed, and not a current source, because no one measures the current in volts, but you can’t say that. It would be most accurate to say - "DC power supply 6 volts", and you can also write "power supply = 6 V" then the symbol "=" will tell us that this is a direct voltage, and in no case variable. However, even here we can sometimes "make mistakes" - language is language.

To understand all this, let us recall the exact definitions from the reference book (memorizing them is very useful). So, the current, or rather, its value, is the amount of charge passing through the conductor section per unit time: I = Qlt. The unit of current is called "ampere" and its dimension is coulombs per second. Knowing this fact will be useful to us later. Where the story with voltage will be more confusing - the voltage value is the potential difference between two points of matter. It is measured in volts, and the unit of measure is the joule.
on a pendant. Why this is so is easy to understand when you delve into understanding the exact definition of voltage: 1 volt is such a potential difference at which the movement of a charge of 1 coulomb will require an expenditure of energy, which will be equal to 1 joule.

All this can be perfectly imagined by comparing a conductor and a pipe through which water flows. Using such a comparison, we see that the magnitude of the current can be easily imagined as the amount of water flowing per second (this is a wonderful analogy in its accuracy), while the voltage is like the difference in pressure at the outlet and inlet of our pipe. Usually the pipe ends with an open drain, so the outlet pressure will be equal to atmospheric pressure and can be taken as a reference level. In the same way, in electrical circuits there is a common wire (or "common bus" - for short it is called "ground", although this is incorrect, the potential of which is taken as zero, and relative to which all voltages in the circuit are measured. Usually (but not always! ) the negative terminal of the main power supply of the circuit is taken as a common wire.

So, back to the question of how to distinguish current from voltage? It would be correct to say this: current is the amount of electricity, and voltage is a measure of potential energy. A person who does not understand physics, of course, will begin to shake his head, trying to understand, then you will add: imagine a stone that is falling. If a rock is small (low electricity) but falls from a height (high voltage), then it can create an impact as powerful as a large rock (lots of electricity) falling from a modest height (low voltage).

In fact, the example with a stone is beautiful, but not accurate - a pipe with flowing water reflects the process much more accurately. You need to know that voltage and current are usually interconnected. (I use the word "usually" because in some cases - voltage or current sources - they try to get rid of these connections, even if they never succeed completely.) Yes, yes, if you return to the example with water in a pipe, it is easy to get an idea, as with increasing pressure in the pipe (voltage) the amount of flowing water (current) increases. In other words, why do we have to use pumps? It is more difficult to imagine exactly the inverse relationship - how the current can affect the voltage. To do this, you need to understand the very essence of resistance.

In the first half of the nineteenth century, physicists did not know how to characterize the dependence of current on voltage. This is a simple explanation. Try to find out experimentally what this dependence looks like.

Only thanks to the talent of Georg Ohm, it was possible to see the true nature of resistance behind all the thickets and obstacles. That is, to deduce that the dependence of current on voltage can be described by the formula: I \u003d U / R. The value of resistance R depends on the material from which the conductor is made and on the external conditions in the environment, especially on temperature.

Current is the directed movement of electrons (charged particles). It occurs if there is a potential difference in the circuit, that is, on one side of the conductor of electric current, an excess of charged particles, and on the other, their lack. The potential difference that allows electric current to flow through a conductor is voltage. Without voltage, there will be no electric current.

In physics, this relationship is expressed by the formula I \u003d U / R, where I is the current strength in the conductor, U is the voltage at the ends of this electrical circuit, and R is the resistance of this circuit. The higher the voltage in the circuit, the more charged particles will pass through it and vice versa.

Current and voltage are quantitative parameters used in electrical circuits. Most often, these values ​​​​change over time, otherwise there would be no point in the operation of the electrical circuit.

Voltage

Conventionally, the voltage is indicated by the letter U. The work done to move a unit of charge from a point of low potential to a point of high potential is the voltage between these two points. In other words, this is the energy released after the transition of a unit of charge from a high potential to a small one.

Voltage can also be called the potential difference, as well as the electromotive force. This parameter is measured in volts. To move 1 coulomb of charge between two points that have a voltage of 1 volt, you need to do 1 joule of work. Coulombs measure electric charges. 1 pendant is equal to the charge of 6x10 18 electrons.

Voltage is divided into several types, depending on the types of current.

• Constant pressure . It is present in electrostatic circuits and DC circuits.
• AC voltage . This type of voltage is available in circuits with sinusoidal and alternating currents. In the case of a sinusoidal current, voltage characteristics such as:
  voltage fluctuation amplitude is its maximum deviation from the x-axis;
  instant voltage, which is expressed at a certain point in time;
  operating voltage, is determined by the active work of the 1st half-cycle;
  medium rectified voltage, determined by the modulus of the rectified voltage for one harmonic period.

When transmitting electricity through overhead lines, the arrangement of supports and their dimensions depend on the magnitude of the applied voltage. The voltage between phases is called line voltage , and the voltage between ground and each of the phases is phase voltage . This rule applies to all types of overhead lines. In Russia, in household electrical networks, the standard is a three-phase voltage with a linear voltage of 380 volts, and a phase voltage value of 220 volts.

Electricity

The current in an electrical circuit is the speed of electrons at a certain point, measured in amperes, and is indicated on the diagrams by the letter " I". Derived units of the ampere are also used with the appropriate prefixes milli-, micro-, nano, etc. A current of 1 ampere is generated by moving a unit of charge of 1 coulomb in 1 second.

Conventionally, it is considered that the current flows in the direction from the positive potential to the negative one. However, from the course of physics it is known that the electron moves in the opposite direction.

You need to know that the voltage is measured between 2 points on the circuit, and the current flows through one specific point of the circuit, or through its element. Therefore, if someone uses the expression "voltage in resistance", then this is incorrect and illiterate. But often we are talking about voltage at a certain point in the circuit. This refers to the voltage between ground and this point.

Voltage is formed from the impact on electrical charges in generators and other devices. Current is generated by applying voltage to two points in a circuit.

To understand what current and voltage are, it would be more correct to use. On it you can see the current and voltage, which change their values ​​over time. In practice, the elements of an electrical circuit are connected by conductors. At certain points, the circuit elements have their own voltage value.

Current and voltage obey the rules:

• The sum of the currents entering the point is equal to the sum of the currents leaving the point (charge conservation rule). Such a rule is Kirchhoff's law for current. The point of entry and exit of current in this case is called a node. A consequence of this law is the following statement: in a series electrical circuit of a group of elements, the current for all points is the same.
• In a parallel circuit of elements, the voltage across all elements is the same. In other words, the sum of voltage drops in a closed circuit is zero. This Kirchhoff's law applies to stresses.
• The work done per unit time by the circuit (power) is expressed as follows: P \u003d U * I. Power is measured in watts. 1 joule of work done in 1 second is equal to 1 watt. Power is distributed in the form of heat, is spent on mechanical work (in electric motors), is converted into radiation of various types, and accumulates in tanks or batteries. When designing complex electrical systems, one of the challenges is the thermal load of the system.

Electric current characteristic

A prerequisite for the existence of current in an electrical circuit is a closed circuit. If the circuit breaks, then the current stops.

Everything in electrical engineering works on this principle. They break the electrical circuit with moving mechanical contacts, and this stops the flow of current, turning off the device.

In the energy industry, electric current occurs inside current conductors, which are made in the form of tires, and other parts that conduct current.

There are also other ways to create an internal current in:

• Liquids and gases due to the movement of charged ions.
• Vacuum, gas and air using thermionic emission.
• due to the movement of charge carriers.

Conditions for the occurrence of electric current

• Heating conductors (not superconductors).
• Application to charge carriers of potential difference.
• Chemical reaction with the release of new substances.
• The effect of a magnetic field on a conductor.

Current Waveforms

• Straight line.
• Variable harmonic sine wave.
• A meander that looks like a sine wave, but has sharp corners (sometimes the corners can be smoothed).
• A pulsating form of one direction, with an amplitude that fluctuates from zero to the largest value according to a certain law.

Types of work of electric current

• Light emitted by lighting devices.
• Generating heat with heating elements.
• Mechanical work (rotation of electric motors, action of other electrical devices).
• Creation of electromagnetic radiation.

Negative phenomena caused by electric current

• Overheating of contacts and current-carrying parts.
• The occurrence of eddy currents in the cores of electrical devices.
• Electromagnetic radiation to the external environment.

The creators of electrical devices and various circuits when designing must take into account the above properties of electric current in their designs. For example, the harmful effect of eddy currents in electric motors, transformers and generators is reduced by blending the cores used to transmit magnetic fluxes. Core blending is its manufacture not from a single piece of metal, but from a set of separate thin plates of special electrical steel.

But, on the other hand, eddy currents are used to operate microwave ovens, ovens, operating on the principle of magnetic induction. Therefore, we can say that eddy currents are not only harmful, but also beneficial.

An alternating current with a signal in the form of a sinusoid can vary in frequency of oscillation per unit of time. In our country, the industrial current frequency of electrical devices is standard, and is equal to 50 hertz. In some countries, the current frequency is 60 hertz.

For various purposes in electrical engineering and radio engineering, other frequency values ​​\u200b\u200bare used:

• Low frequency signals with lower current frequency.
• High frequency signals, which are much higher than the current frequency of industrial use.

It is believed that electric current occurs when electrons move inside a conductor, so it is called conduction current. But there is another type of electric current, which is called convection. It occurs when charged macrobodies move, for example, raindrops.

Electric current in metals

The movement of electrons under the influence of a constant force on them is compared with a parachutist who descends to the ground. In these two cases, uniform motion occurs. The force of gravity acts on the skydiver, and the force of air resistance opposes it. The electric field force acts on the movement of electrons, and the ions of the crystal lattices resist this movement. The average speed of the electrons reaches a constant value, as well as the speed of the skydiver.

In a metal conductor, the speed of one electron is 0.1 mm per second, and the speed of an electric current is about 300,000 km per second. This is because electric current flows only where voltage is applied to the charged particles. Therefore, a high current flow rate is achieved.

When moving electrons in a crystal lattice, there is the following regularity. The electrons do not collide with all the ions they meet, but only with every tenth of them. This is explained by the laws of quantum mechanics, which can be simplified as follows.

The movement of electrons is hindered by large ions that resist. This is especially noticeable when metals are heated, when heavy ions "swing", increase in size and reduce the electrical conductivity of the crystal lattices of the conductor. Therefore, when metals are heated, their resistance always increases. As the temperature decreases, the electrical conductivity increases. By reducing the temperature of the metal to absolute zero, the effect of superconductivity can be achieved.

What is voltage and current?

Today we will talk about the most basic concepts of current strength, voltage, without a general understanding of which it is impossible to build any electrical device.

So what is tension?

Simply put voltage- potential difference between two points in an electrical circuit, measured in volts. It is worth noting that voltage is always measured between two points! That is, when they say that the voltage on the controller leg is 3 Volts, it means that the potential difference between the controller leg and the ground is the same 3 Volts.

Earth (Mass, Zero) is a point in an electrical circuit with a potential of 0 Volts. However, it is worth noting that voltage is not always measured relative to ground. For example, by measuring the voltage between the two terminals of the controller, we will get the difference in the electrical potentials of these circuit points. That is, if there are 3 Volts on one leg (That is, this point has a potential of 3 Volts relative to the ground), and on the second 5 Volts (Again, the potential relative to the ground), we will get a voltage value equal to 2 volts, which is equal to the potential difference between points 5 and 3 Volta.

From the concept of voltage follows the next concept - electric current. From the course of general physics, we remember that electric current is the directed movement of charged particles along a conductor, measured in amperes. Charged particles move due to the potential difference between the points. It is generally accepted that current flows from a point with a large charge to a point with a smaller charge. That is, it is the voltage (potential difference) that creates the conditions for the flow of current. In the absence of voltage, current is impossible, that is, there is no current between points with equal potential.

On its way, the current encounters an obstacle in the form of resistance, which prevents its flow. Resistance is measured in ohms. We'll talk more about it in the next lesson. However, the following relationship has long been derived between current, voltage and resistance:

Where I - Current in Amps, U - Voltage in Volts, R - Resistance in Ohms.

This relationship is called Ohm's law. The following conclusions from Ohm's law are also valid:

If you still have questions, ask them in the comments. Only thanks to your questions We will be able to improve the material presented on this site!

That's all, in the next lesson we'll talk about resistance.

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