1. The role of inductance: ** filter, oscillation, delay, notch; image statement: through DC, blocking AC. Inductance is the ratio of the magnetic flux of the wire
to the current that produces this flux when an alternating current is passed through the wire to generate an alternating magnetic flux around the inside of the wire
.
To put it simply, it is to pass DC resistance AC, isolate AC signal, filter or form a resonant
circuit with capacitors, resistors, etc.
The so-called direct current
means that in the direct current circuit, the role of the inductance is equivalent to a wire, which has no effect.
AC resistance
In an AC circuit, the inductance will have impedance, that is, XL, and the current of the entire circuit will become smaller, which will hinder the AC to a certain extent
. When the inductance coil is supplied with alternating current, its own current changes, which causes its own magnetic flux to change and induce electromotive
force. This phenomenon is called self-inductance. The direction of self-inductance current always hinders the current change that causes self-inductance.
When it is strong, the direction of the self-induction current is opposite to that of the alternating current, and when the alternating current is weakened, the self-induction current is in the same direction as the alternating current,
so that it has a blocking effect on the alternating current.
Working principle of inductance Inductance is the ratio of
the magnetic flux of the wire to the current that produces this flux when an alternating current is passed through the wire .
When a DC current is passed through the inductor, there are only fixed magnetic lines of force around it, which do not
change with time; but when an alternating current is passed through the coil, there will be magnetic lines of force around it that change with time.
According to Faraday's law of electromagnetic induction: magnetism generates electricity, the changing magnetic lines of force will generate an induced potential at both ends of the coil,
which is equivalent to a "new power supply". When a closed loop is formed, the induced potential will generate an induced current
. According to Lenz's law, it is known that the total amount of magnetic force lines generated by induced current should try to prevent the change of magnetic force lines. The change of the magnetic field line
comes from the change of the external AC power supply, so from the objective effect, the inductance coil has
the characteristic of preventing the current change in the AC circuit. The inductance coil has characteristics similar to the inertia in mechanics. It is called "self-induction" in electricity.
Usually will occur at the moment when the knife switch is pulled or turned on. This self-induction phenomenon produces
caused by high induced potential .
2. The relationship between the current and voltage of the DC inductor coil
Add a DC voltage U (unit V) to a coil whose original voltage and current are 0, and the current rises gradually from 0. If the resistance of the coil is R (unit Ω), then the current reaches U/R after an infinite time (Unit A), there is a transition process in the middle, which is an exponential curve, unlike pure resistance, the current suddenly reaches U/R. Let the inductance of the coil be L (unit H), then L/R is called the time constant, and its unit is S (second), expressed by the Greek letter τ (pronounced tao). When L/R=3τ, when t= At 3τ, the current rises to 95% of U/R, and it is generally considered that the rise has been completed.
Because L is generally very small and τ is also very small, it can be considered that the electric current reaches U/R when it is connected, that is, I=U/R. In the figure below, i is the current, e is a constant, and e≈2.718.
