Alternating current - current with varyingin time direction and strength. Those currents, which vary only in magnitude, are called pulsating. In industry and everyday life, an alternating sinusoidal current is most often used.
Convert DC to ACelectric can be performed as follows. We place a coil of wire in a uniform constant magnetic field. With uniform rotation of this coil around the axis, the magnetic flux will change continuously in both magnitude and direction. Consequently, according to the law of electromagnetic induction, a variable in the direction and magnitude of the electromotive force (EMF) is formed in the turn. If such a turn is attached to an external circuit, then in it we obtain an alternating electric current.
Когда плоскость вращающегося витка становится is perpendicular to the lines of force of a given magnetic field, the magnetic flux passing through it is the largest (Φ = Φmax), and the rate of its change is zero (ΔΦ / Δt = 0), because, passing through this position, the conductors of the coil slip along the force lines lines of the field without intersecting them. So, the EMF of induction, formed in the turn, will become zero (E = 0).
When the plane of the turn is parallel to the power(Φ = 0), the rate of its change in this position is the greatest ((ΔΦ / Δt) max), since the conductors of the turn move perpendicularly relative to the lines of force.
The emf, which in this case appears in the revolution, hasthe highest value (E = Emax). With further rotation of the coil, the rate of change of the flux penetrating the coil will increase; hence, the EMF will increase in absolute value from 0 to Emax. Thus, the level of EMF induction in a rotating coil changes from -Emax to + Emax in one turn.
Open the coil of the wire and attach it to thean oscilloscope. When the turn rotates in a magnetic field, the oscilloscope will record all the current changes, along which it will be possible to judge the change in the electromotive force in the revolution during one turn.
The current that appears in the revolution when it is uniformly reversed in a uniform magnetic field, as shown by the oscillogram, varies sinusoidally. This current is called alternating sinusoidal.
The time interval for which the electromotive force performs a single oscillation is called the period of alternating current.
The letter designation of the oscillation period is T. The number of oscillations per second is the frequency of the current, which is denoted by the letter f. Its unit of measure is hertz (Hz):
f = 1 / T, or T = 1 / f.
If the EMF value at some arbitrary moment(its instantaneous value), and the largest value (amplitude) by Emax, the law expressing the dependence of e on time in the case of a sinusoidal current can be expressed in the form of the following expression:
e = Emax˖sin (2 / T) t.
In most countries, an alternating current with a frequency of 50 Hz, a period duration of 0.02 seconds is used in industry and at home.
Obtaining an alternating electric current fromMechanical energy is carried out with the help of special machines, which are called generators. The principle of their work is based on the law of electromagnetic induction. The simplest circuit of the generator can be represented in the form of a frame rotating around an axis in the magnetic field of an electromagnet or a permanent magnet. When the frame is rotated, a variable electromotive force is produced in it. By connecting the frame to the external circuit, we obtain an alternating electric current. An alternating current generator having a fixed magnetic system and rotating turns is constructed quite rarely.
Almost in all such generators, the winding (anchor) is fixed, and the magnetic system (inductor) rotates. The real part of the generator is called the stator, and the movable part is the rotor.
