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The magnetic field is characterized by a vector of magnetic induction V. Vektor is sent to magnetic induction along a piece of the conductor with current when this piece is focused so that it from a magnetic field is not affected by force. The size of the module of a vector of magnetic induction is equal

For calculation of magnetic induction of a separate element of current taking into account the principle of superposition, we will consider the conductor section S, length of dL on which charged particles with charges of q and concentration of n move

Thus, the magnetic induction of a field of direct current is defined by a formula (1, and it can 'be also used for calculation of a field of the conductor with current of final length provided that R distance a little in comparison with length of the conductor.

Round conductors with current and permanent magnets the magnetic field is formed. When placing in a magnetic field of the conductor force which size is proportional to length of this piece in space works.

current dL and a point And and consequently, they form a symmetric conic fan. The geometrical sum of all vectors of dB is in number equal to the algebraic sum of projections of all vectors to axis X. The projection of a vector of d B x to axis X is equal

where I - intensity of this sound, Io - initial intensity (I1o accept equal 10-12 W/m so the audibility threshold with a frequency of 10 Hz lies at zero level, W - watt, a power unit). Unit of level of loudness of L is called White (. Usually use by 10 times smaller units - decibels ((Tikhiq conversation - 40 dB, gromkfz the speech - 70 dB., noise of the plane at distance of Z rv-130 D.