DC current and alternating current.
DC current
A circuit is a closed conductive path through which electrons flow from the power supply to the load and back to the power source, how is the power supply a DC power supply, the electrons in the circuit flow in only one direction, producing a direct current (DC).
Alternating current
Another type of power supply commonly used in electronics is an alternating power supply, which produces an alternating current (AC) that periodically changes direction.
In an alternating circuit, not only does the direction of the current change periodically, but also the polarity of the voltage.
The AC circuit is excited by a sinusoidal power supply that produces a sine wave that changes periodically. Depending on the application, the frequency of the sine wave can vary from a few hertz to a few gigahertz.
The positive and negative changes of voltage and current relative to the coordinate axis of OV 0A indicate that the electrodynamic direction of the power supply is changing, so it causes the polarity of the voltage source and the direction of the current to change.
Formation of alternating currents
The most presumptuous way to generate a sine wave signal is to apply the principle of electromagnetic induction, i.e. to an alternator (or converter).
A simple alternator consists of magnets and coils. The coil is placed between the N and S poles of the magnet and can be rotated around the shaft.
As the coil rotates in the magnetic field, the magnetic flux through the coil changes continuously, and the charge in the coil moves by the force of the magnetic field, thus forming an induced voltage at both ends of the coil.
The actual alternator structure is much more complex, but it is based on the principle of electromagnetic induction.
Other methods of generating alternating currents are the use of frequency converters (e.g., amplifiers) or the use of a DC-excited oscillation circuit consisting of an inductor and a capacitor.
The importance of alternating currents
In electronics, the main reason why sine wave signals are widely used is that the alternator can easily convert periodic mechanical movements into induced currentsAnother important reason is that the integral or differential of a sinusoidal quantity is derived from a sinusoidal quantity.
An important benefit of using alternating current is that the voltage can be increased or decreased by using a transformer to reduce current losses in transmission.
Since the transformer cannot be used in the DC circuit, the voltage change in the DC circuit is quite difficult, and there is often resistance loss, and the resistance loss of a single transformer in the AC voltage conversion process is very small.
Water simulation system for AC circuits
This simulation system uses a manual crank to drive the cam mechanism to move the piston up and down.
In a water simulation system, water particles sway back and forth as the crank turns.
There are effects in AC circuits that correspond to water simulation systems, but they are a bit more complex.
It can be assumed that inside the conductor, the drift velocity of the free electrons vibrates back and forth in a sinusoidal manner, and the actual drift velocity and drift distance are very small, generally in the micron range, and are related to the nature of the conductor and the magnitude of the supply voltage.
It is theorized that the average displacement of electrons is zero in a period, which alone does not contradict the random thermal velocity of individual electrons.
Last test questions
Problem: Find the voltage between each point in the diagram and the ground point
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