Is it possible to imagine your life withoutelectricity? Modern man tightly surrounded himself with household appliances that help in life. We can no longer imagine ourselves and our lives without intelligent domestic helpers.
In technology, more often switch to the use of electricity. Even transport is gradually transferred to electric motors, which allows to reduce the significant harm to nature.
Today we will try to answer the following questions:
At the dawn of the study of electricity, he was givenfriction of one body about another. A larger reserve of charge could be obtained during a thunderstorm, using a natural discharge - a lightning bolt. It is known that this method cost a lifetime to the student of MV Lomonosov, Richter.
The charge itself is difficult to use and irrational. It is necessary to obtain its directional motion - electric current. Current properties:
They are used in everyday life and technology. A necessary condition for the existence of a current is the presence of a current source, free electric charges, and a closed conductor.
In 1792 the famous Italian physicist, physiologistand inventor Alessandro Volta was interested in the findings of compatriot Luigi Galvani about the nature of current pulses in animal organs. A long observation of the behavior of the feet of frogs fixed on metal hooks allowed him to conclude that the source of electricity is not a living organism, but a contact of dissimilar metals. It is this circumstance that facilitates the flow of electricity, and the reaction of the nerve endings is only the physiological action of the current.
A unique discovery led to the creation of the firstthe world of a constant current source, called "Volta Pole". Heterogeneous metals (Volta argued that they should be removed from each other in a series of chemical elements) are paved with paper impregnated with a liquid "conductor of the second kind."
This device became the first constant voltage source. The unit for measuring the electrical voltage perpetuated the name Alessandro Volta.
The main element of the electrical circuit is the sourcecurrent. Its purpose is to create an electric field, under the action of which free charged particles (electrons, ions) come in directional motion. The charges accumulated on separate elements of the source (they are called poles) have different signs. The charge itself is redistributed inside the source under the action of forces of non-electrical nature (mechanical, chemical, magnetic, thermal, etc.). An electric field created by poles outside the current source, performs work on the movement of charge in a closed conductor. Alessandro Volta spoke of the need for a closed circuit to create a constant current.
Since in sources under the action of forcesnon-electric nature, the charge moves, so you can say that these forces are doing the work. We call them extraneous. The ratio of the work of external forces on the transfer of charge inside the current source to the magnitude of the charge is called the electromotive force.
The mathematical notation for this relation is:
where E is the electromotive force (EMF), Aart. - the work of external forces, q - the charge carried by external forces in the source.
EMF characterizes the ability of the source to create a current, but the main characteristic of the source is sometimes considered to be the electrical voltage (potential difference).
The ratio of the field work on the movement of charge in the conductor to the charge value was called the electric voltage.
To determine it, you need the amount of field workdivided by the magnitude of the charge. Let A be the work accomplished by the electric field of the current source in charge displacement q. U is the electrical voltage. Mathematical notation of the corresponding formula:
Like any physical quantity, the voltage hasunit of measurement. How is the voltage measured? According to the name of the inventor of the world's first direct current source Alessandro Volta, this value was given its own unit of measurement. In an international system, the voltage is measured in volts (V).
A voltage of 1 V is considered to be the voltage of the electric field, which performs work in 1 J for charge transfer in 1 Cl.
In the basic units of the SI system, the unit for measuring the electrical voltage:
Why is it not enough, characterizing the current, to introducethe concept of current strength? Let's conduct a mental experiment. Let's take two different lamps: an ordinary household lamp and a lamp from a flashlight. When connected to different sources of current (city network and battery), you can get an absolutely identical value of the current strength. At the same time, the household lamp gives more light, that is, the current work in it is much larger.
Different sources of current have different voltages. Therefore, this quantity is extremely necessary.
Understanding the physical meaning of electricalvoltage comes, if you look into an interesting analogy. In communicating vessels, liquid flows from the tube into the tube if there is a pressure difference in them. The liquid flow stops when the pressures are equal.
If the fluid current is compared with the flow of electric charge, then the pressure difference of the liquid columns plays the same role as the potential difference in the current source.
As long as there are processes within the current source,accompanying the redistribution of charge at the poles, it is able to create a current in the conductor. The voltage of the electric current is measured in volts, the pressure difference has a unit of measure - pascal.
Electric current, periodically changing itsdirection, is called a variable. It is created by a source of an alternating voltage. Most often it's a generator. Let's try to explain: in what is measured the AC voltage?
The very principle of current generation is based on the phenomenonelectromagnetic induction. Rotation of a closed loop in a magnetic field leads to the appearance of a potential difference in the conductor. Voltage is measured in volts and in the case of a varying current.
Can we say that the voltage does not change?Obviously, due to a change in the angle between the plane of the contour and the normal to it, the created voltage changes with time. Its value grows from zero to some maximum value, then drops again to zero. Talk about a certain amount is not necessary. Enter the so-called effective voltage value:
Device for measuring electrical voltage -voltmeter. The principle of its operation is based on the interaction of the circuit with the current and the magnetic field of a permanent magnet. It is known that the current loop rotates in a magnetic field. Depending on the magnitude of the current in the circuit, the angle of rotation changes.
If you attach an arrow to the outline, itdeviates from the zero value when the current flows in the circuit (more often the coil). Depending on how the voltage is measured, the scale of the instrument is calibrated. The use of longitudinal and multiple values is possible.
In the case of low values, the electrical voltage is measured in millivolts or microvolts. On the contrary, multiple units are used in high-voltage networks.
Any voltmeter is connected in parallel tosection of the circuit on which the voltage is measured. The main property of the device circuit can be called high ohmic resistance. The voltmeter, no matter what the voltage is measured, should not affect the current in the circuit. A small current is passed through it, which does not significantly affect the fundamental value.
Physical device | Voltage at its contacts, V |
Volt post | 1,1 |
Pocket flashlight battery | 1,5 |
Alkaline battery | 1,25 |
Acid battery | 2 |
City network | 220 |
High-voltage transmission lines | 500 000 |
Between the clouds in a thunderstorm | Up to 100 000 000 |
To use the voltmeter effectively, you should learn how to use it. A curious experimenter can be advised to apply to school teachers.
School physics classrooms are equipped with laboratory and demonstration instruments for measuring voltages.
Operate any voltmeter with caution, following the simple rules:
The effect of an electric current can be unsafe for a person. A voltage less than 24 V is considered harmless.
The effect of the current under the voltage of the city network (220 V) is quite noticeable. Touching the exposed contacts is accompanied by a significant "current shock".
Voltage during a thunderstorm passes such a high current through the human body, which threatens him with a lethal outcome. Do not risk your life and health.
