Did you imagine your life without electricity?Modern man has surrounded himself with a tightly appliances that help in life.We can not imagine myself and my life without smart household helpers.
The technique is increasingly moving to the use of electricity.Even transport is gradually transferred to the electric motors, which reduces significantly the damage caused by nature.
Today we will try to answer the following questions:
- What is electricity?
- What is the voltage?
- How to stress?
- What voltage is measured?
What is current?
At the beginning of his study of electricity obtained by friction of one body against another.A large supply of the charge could be obtained during a thunderstorm, using the natural discharge - lightning.It is known that this method is cost student life Lomonosov - Richter.
charge itself is difficult and impractical to use.Need to get his direction - an electric current.Current Properties:
- heat conductor;
- chemical action;
- mechanical action;
- magnetic effect.
They are used in everyday life and technology.A necessary condition for the existence of the current feel the presence of the current source of free electric charges and closed conductor.
Background
In 1792, the famous Italian physicist and physiologist and inventor Alessandro Volta interested in the conclusions of compatriot Luigi Galvani on the nature of the current pulses in the bodies of animals.Long-term observation of the behavior of frogs legs attached to a metal hook, allowing him to conclude that the source of electricity is not a living organism, and the contact of dissimilar metals.This circumstance favors the electricity, and the reaction of nerve endings - only the physiological effect of the current.
unique discovery led to the creation of the world's first DC power source, called "voltaic pile".Dissimilar metals (Volta argued that they should be removed from each other in a series of chemical elements) laid paper impregnated with liquid, "the conductor of the second kind."
This device became the first DC power supply.A unit of electrical voltage has immortalized the name of Alessandro Volta.
Source DC
main element of an electrical circuit - current source.Its purpose - to create an electric field, which is under the influence of free charged particles (electrons, ions) come to the driving direction.Accumulate on the individual elements of the source of charges (called poles) have different signs.Charge redistributes itself within the source under the forces of nature nonelectrical (mechanical, chemical, magnetic, thermal, etc.).An electric field is created by the poles of the current source, produces work of moving a charge in a closed conductor.On the need to create a closed-loop DC has said Alessandro Volta.
Since the sources under the forces of nature is a movement of non-electrical charge, so it can be argued that these forces do work.Let us call them by.The ratio of the work of external forces on the charge transfer within the power supply to the magnitude of the charge is called electromotive force.
mathematical notation of this relationship:
- Ε = Ast: q,
where E - electromotive force (EMF), Ast - the work of external forces, q - the charge carried by the third-party source.
EMF describes the ability to create a current source, but the main characteristic is sometimes considered a source of electrical voltage (potential difference).
voltage
respect of the field of movement of charge in the conductor to the magnitude of the charge has been called electric voltage.
to define it, you need to value the work of the field divided by the amount of the charge.Let A - the work done by the electric field of the power source to move the charge q.U - voltage.The mathematical formula corresponding entry:
- U = A: q.
Like any physical quantity, unit of measure is the voltage.What is the voltage measured?By the name of the inventor of the world's first DC source Alessandro Volta this value given their own unit.The international system voltage is measured in volts (V).
tension in 1 is considered to be the electric field does work in 1 John on the movement of the charge 1 Cl.
- B = J / C = N • m / (A • C) = kg • m / (A • c3).
The basic units of the SI unit of measurement voltage:
- kg • m / (A • c3).
required value
Why not sufficient, describing current to introduce the concept of the current?A thought experiment.Take two different lamps: ordinary household lamp and the lamp of the flashlight.When you connect them to different power sources (urban network and battery), you can get exactly the same amperage.At the same time, household lamp produces more light, that is, the current work it is much more.
Different sources of electricity have different voltages.Therefore, this value is essential.
useful analogy
understanding of the physical meaning of voltage comes, if we look at an interesting analogy.In the communicating vessels the liquid flows from the tube into the tube, if there is a difference in these pressures.Fluid flow is terminated in case of equality of pressures.
If fluid flow compared with the passage of an electric charge, then the difference in head pressure plays the same role as the potential difference of the power source.
While inside the power supply there are processes that accompany the redistribution of charge at the poles, it is able to create a current in the conductor.Voltage electrical current is measured in volts, the pressure difference is the unit of measurement - Pascal.
AC
electric current periodically changes direction is called a variable.Create a source of alternating voltage.Most often it is a generator.Let's try to clarify: what is measured by the AC voltage?
The principle of power generation is based on the phenomenon of electromagnetic induction.The rotation of the closed loop in the magnetic field leads to the appearance of a potential difference in a conductor.Voltage is measured in volts and in the case of changing the current.
Can we say that the tension does not change?Obviously, due to changes in the angle between the plane and the normal contour thereto generated voltage varies with time.Its value increases from zero to a maximum value and then falls again to zero.To speak of a certain value is not necessary.Enter the so-called actual voltage:
- Ud = U: √2.
What instrument measures the voltage?
instrument for measuring electrical voltage - voltmeter.Its principle of operation is based on the interaction of loop current and magnetic field of the permanent magnet.It is known that the current loop is rotated in a magnetic field.Depending on the magnitude of the current in the loop varies the angle of rotation.
If the contour attach arrow, it deviates from zero when the current flows in the loop (more coil).Depending on what the voltage is measured, a scale calibrated instrument.Perhaps the use of longitudinal and multiples.
In the case of low values of the voltage is measured in millivolts or microvolts.On the contrary, in high-voltage networks using multiple units.
Any voltmeter is connected in parallel to the circuit section, which is measured voltage.The main feature of the circuit device can be called a high ohmic resistance.Voltmeter, regardless of what the voltage is measured, should not affect the current in the circuit.As it passes negligible current, it does not affect the basic meaning.
Table stresses
| physical devices | voltage at its contacts, |
| Voltaic pile | 1,1 |
| battery flashlight | 1,5 |
| alkaline batteries | 1,25 |
| acid batteries | 2 |
| Urban Network | 220 |
| power line | 500,000 |
| between the clouds in a thunderstorm | Up to 100 million |
Practical application voltmeter
To make effective use of the voltmeter should learn how to use.Curious experimenter may wish to consult with school teachers.
classrooms are equipped physics laboratory and demonstration devices for measuring voltages.
Operate any voltmeter is carefully observing the simple rules:
- voltmeter has a maximum limit of measurement.This is the highest value in its scale.It is not necessary to connect it to the circuit element having a larger strain.
- If there is no other source, or a voltmeter, you can use the system of additional resistances.At this scale of the voltmeter must also be changed.
- The DC electric circuit connected as specified by the sign of the charge on its terminals.The positive terminal of the power source must be connected to the positive terminal of the voltmeter negative - to negative.If you confuse the instrument needle may bend, which is extremely undesirable.
- All connections are made only to the de-energized circuit.
Harmful
electric current may harm human.It is considered harmless voltage less than 24 V.
Action energized current urban network (220) is enough tangible.Touching the exposed contacts accompanied by a significant "electric shock".
voltage during a thunderstorm passes such a high current through the human body, which threatens his death.Do not risk your life and health.
