There are laws which processes occurring in electric chains submit. For understanding of work of electric schemes it is necessary to know these laws. Usually if the electric scheme and elements used in it is known, to find out its working capacity it is possible having learned currents proceeding on these elements and voltage on them. Failure of an element of the electric scheme can occur at excess of a current proceeding on it or voltage on it. All elements on which the electric current proceeds possess active resistance which is factor connecting a current and pressure, that is knowing resistance of an element and a current proceeding on it (pressure on it) it is possible to calculate pressure on it (a current proceeding on it). Communication between a current, voltage and resistance expresses the Ohm law. The Ohm law sounds as follows: the current strength on a chain site is equal to the voltage relation on this site to its resistance. The Ohm law registers in the form of the formula:
Where I - a current (current strength) of a site of an electric chain, U - pressure on it,
R - resistance of a site of an electric chain.
For convenience, on electric schemes the current is represented arrow on a conductor, and an arrow the beginning and which end specify pressure in points between which there is a pressure. It is accepted to accept for a positive direction of a current a direction from a point with high potential to a point with smaller potential (in real chains it not always so). If to direct arrow on a conductor to other party that value of a current should change a sign on opposite (for pressure also). The rectangle designates the resistor.