Electric current - ordered motion electrocharge.It can be prepared, for example, in a conductor which connects the body of charged and uncharged.However, this current will cease as soon as the potential difference of these bodies will be zero.The orderly motion of charges (electric current) will exist in the conductor connecting the plates of a charged capacitor.In this case, the current is accompanied by neutralizing the charges in the plates of the capacitor, and continues until the potential difference of the capacitor plates will not be zero.
These examples show that the electric current in the conductor occurs only in the presence of different conductors at the ends of potentials. E. When it has an electric field.
But the examples considered the current can not be long, because in the process of moving the charge potentials bodies quickly equalized and the electric field in the conductor disappears.
Therefore, for the current necessary to maintain the ends of the conductor different potentials.To do this, the charge transfer from one body to another back along the other conductor, forming a closed circuit for this.However, under the action of the electric field of such charge transfer is impossible, since the potential of the second body is smaller than a first potential.Therefore, the transfer is only possible by the non-electrical origin.The presence of such a force to provide a source current in the circuit.
Forces in the current source, charge transfer from the body to the lower potential of the body with great potential and perform at the same job.Consequently, the power source must have energy.
current sources are electric machines, galvanic cells, batteries, generators and so on. D.
Thus, the basic conditions for the emergence of electric current: the presence of a source of current and closed circuit.
passage of current in the circuit is accompanied by a number legkonablyudaemyh phenomena.For example, some fluids during the passage through them of current observed release of a substance at the electrodes lowered into the liquid.The current in gases is often accompanied by glowing gas, and so on. D. The electric current in gases and vacuum studied the great French physicist and mathematician - André Marie Ampere, thanks to which we now know the nature of such phenomena.
As is known, a vacuum - the best insulator, t. E. The space from which the exhausted air.
but can receive electric current in a vacuum, for which it is necessary to add to the charge carriers.
take the vessel from which air is pumped out.To this vessel are soldered two metal plates - two electrodes.One A (anode) connected to a positive power source, the other K (cathode) - negative.The voltage between the anode and cathode is sufficient to make 80 - 100 W.
included in the circuit sensitive milliammeter.The device shows no current;this indicates that the electric current does not exist in vacuo.
altering experience.As the cathode wire soldered into the vessel - the thread derived from the outward ends.This thread will remain cathode.Using another power source inflame it.We note that as soon as the thread is heating up, the device is included in the circuit shows the electric current in a vacuum, and the more, the more tense the thread.Hence, the thread ensures that when heated under vacuum of the charged particles, it is their source.
As charged, these particles?The answer to this question can be experience.Alternating poles have soldered electrodes into a vessel - the thread will make the anode and the opposite pole - the cathode.Although the thread tense and sends charged particles in a vacuum, there is no current.
This implies that these particles are negatively charged because they are repelled by the electrode A when it is negatively charged.
What are these particles?
According to the electron theory, the free electrons in the metal are in chaotic motion.When the glow filament movement is enhanced.However, some electrons gaining energy, which is enough to carry the output emitted from the filament to form around it, "electron cloud".When between the filament and the anode is formed the electric field, the electrons fly toward the electrode A, if it is connected to the positive pole of the battery, and repelled back to the filament when it is connected to the negative pole, t. E. Has a charge of the same name with electrons.
Thus, an electric current in a vacuum - a directed flow of electrons.
