Electronic devices

The invention of vacuum tubes at the beginning of XX century allowed to amplify the electrical signals. This discovery was the beginning of rapid development of electronics.
Many components of electronic circuits are simple resistors and capacitors. A resistor is a conductor, which flows into the chain of a certain (depending on resistance) quantity current. Fixed resistors are made of graphite or glass tubes that are inside or outside of the insulating material. In variable resistors (which are used, for example, as regulators of the settings in the body and the electronic circuits) of the existing sliding contact to control the resistance.
A typical capacitor is two metal plates separated by a dielectric (air, paper or plastic); placed on the plate the electric charge remains on the capacitor will not be included in the circuit. Capacitors can be used not only as devices for storing electric charges. For example, using the dielectric between the plates, the current flow cannot, however, change in the voltage on one plate causes a corresponding change in voltage on the other, that is, the capacitor is able to efficiently transmit the AC voltage of the AC, but does not pass full voltage. Therefore, capacitors can be used to separate the variable and constant components of the voltage.