The less commonly used passive components, the humble and mysterious inductor, are the subject of this video. The essence of induction is the tendency of a conductor to resist changes in current. When the current is steady it is invisible, but when the current changes an inductor pushes back. The good old analogy of the water wheel is given to explain the effect of an inductor.
There are three things to note about the effect of an inductor: current increases are delayed, current decreases are delayed, and if there is no change in current there is no noticeable effect. The inductor cannot withstand the current, but it can withstand changes in the current. This resistance effect only occurs when the current changes and is known as “inductive reactance”.
After explaining the behavior of an inductor, the video takes a closer look at how a typical inductor coil actually achieves this. The basic idea is that the inductor stores energy in a magnetic field, and it takes some time to charge or discharge this field, taking into account the delay in the current being sensed.
There is a warning about high voltages that can be seen when the power to an inductor is suddenly turned off. Normally a circuit contains snubber circuits or flyback diodes to help control such effects that could otherwise damage components or lead to an electric shock.
[Prof MAD] spends the rest of the video doing some math explaining how the voltage across an inductor is proportional to the rate at which the current changes over time (the first derivative of current versus time). The induction can then be defined as a constant of proportionality (L). This is the voltage that appears across a coil when the current changes at 1 ampere per second, which opposes the change. The unit is volt-second-per-ampere (VsA-1) known as the Henry, named in honor of the American physicist Joseph Hendrik.
Induction can sometimes be put to good use in circuits, but just as often it is unwanted parasitic induction whose effects must be mitigated. For more information, see: Inductance in PCB Layout: The Good, The Bad, And The Fugly.
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