Electronic Basics #37: What is Impedance? (AC Resistance?)

when it comes to creating DC Circuit's like I do in around ninety percent of the cases then the function of the most basic passive components the resistor the inductor and the capacitor is pretty straightforward the resistor like the name implies resists the current flow and thus can be used for example in an led circuits to convert the excess power into heats so that our LED can shine with the correct nominal current flow unless of course someone evil shorts the resistor on the other hand you can find capacitors and inductors in DC circuits as energy storages because the capacitor resists sudden changes in voltage and the inductor sudden changes in current and thus we get a smooth output voltage from for example of power supplies but make sure to watch the individual basics episodes for those three components if you want to learn more about them what is important though is that resistors resist the current flow in a DC Circuit's while inductors and capacitors do not influence the DC current flow unless of course we talk about switch on / off situations but this year is not almighty while looking around us we can see tons of applications where we cut AC voltages most importantly our sinusoidal mains AC voltage so in this video I will tell you about the basics of impedance which in a nutshell is the concept of resistance extended to AC circuits where now inductors and capacitors play an important role as well let's get started [Music] this video is sponsored by jl CPC be one piece of news about them jailed CPC beer will shorten the lead time of green to layer standard PCBs in the near future so feel free to test out their PCB quality and fast delivery speed for low price for the experimental setup I connected my function generator outputs to the inputs of an amplifier this way by varying the frequency and amplitude of the function generator sine wave I get the amplified sine voltage at the output of the amp that can handle a much higher power outputs which means we cannot components up to it for starters let's use this small inductor which features an inductance of around 214 microhenry by connecting it directly to the sine wave which features an RMS voltage of 6 volts and a frequency of 10 kilohertz and observing the occurring current flow with a current clamp we can firstly see that the voltage wave is leading in comparison to the current wave with a phase shift of around 90 degrees and also that an RMS current of 203 milliamps is flowing that means that this time the inductor does not create a short circuits like added with TC it resists the current flow just like a resistor would do and thus this value is measured in ohms as well and is called the inductive reactance this new kind of resistance originates from the effects that the constantly changing magnetic fields of the inductor opposes the current flow which is also the reason why the voltage is leading with a phase angle 1 and by increasing the frequency of the sine voltage we can see how the current RMS value slowly decreases which means our inductive reactance increases with the frequency the final equation for it is 2 pi FL move the frequency and inductance being the most important variable values now if we would replace the inductor with a capacitor which features a capacity of one MOOC of rods and use a frequency of 3 kilo Hertz we can once again observe a phase shift of around 90 degrees but this time the current is leading also we cut an arm as current flow of 110 millions which means just like with the inductor we get a new sort of resistance this time known as capacitive reactance its cause is the constant charge reversal of the electrostatic fields of the capacitor and it's equation once again features the frequency and capacitance as the most important variable values this time though with higher frequency the current flow increases which means the capacitive reactance decreases now if we go back to the plain old resistor and hook it up we can see that it does not create a phase shifts and its resistance and thus current flow is not dependent of the AC frequency it still only got its ohmic resistance and just like that you're now familiar with the reactance of the inductor and capacitor which not only changes the magnitude of the current flow dependent of the frequency but also effects the phase angle between voltage and current and of course we still got our ohmic resistance which only influences the magnitudes and not the face but the question remains what does all of that have to do with impedance well let's imagine we put a 50 ohm resistor and a 1 Mooka farad capacitor in serious to the 3 kilohertz six point one volts sine voltage how can we calculate voltage current and phase angle values simply adding the ohmic resistance to the capacitive reactance and calculating of that would only deliver wrong values and thinking the phase angle would stay at 90 degrees is also incorrect the solution is to turn both values into a complex impedance and calculating with that this one is the polar form of the impedance but also important for calculations is the Cartesian form in its we can see our known values for the resistance and reactions but there's also a J this J is actually the imaginary unit area of the imaginary number system but since I usually refers to current and electronics we stick to the J if we would now draw a complex plane with the x-axis being the real axis and the y axis being the imaginary axis we could now plot our resistance and reactance the resistance is obviously real so we go with a value of 50 ohms to the right the reactance however is imaginary meaning week of 53 arms down and by the way if we would use an inductor instead of the capacitor the direction of the arrow would be inverted so upwards but anyway the now emerging arrow is the impedance vector we've been looking for its angle is required for the face angle and it's magnitudes for the current calculation so according to simple trigonometry here the magnitude equals the root of R squared plus X C squared and the phase angle is arctangent of XC divided by R and by using my trusty olds ti-83 plus I calculated a magnitude of 72 point 9 ohms which equals a current flow of 83 point seven million s and a phase angle of forty six point seven degrees by measuring the corresponding values at the practical circuits we can see that our calculations were actually not too far off they cannot be perfect however because our capacitor itself not only featured capacitance but also a small resistance and even a super tiny inductance those values are known as equivalents serious resistance and equivalence serious inductance and basically build up a complex impedance even without an additional resistor in the case of the capacitor there were rather small but if we would look at a practical inductor then you can see that the previously measured reactance is far from the calculated value meaning it got tons of parasitic resistance and by the way by utilizing a good LCR meter you cannot only measure the capacitance resistance and inductance but also the complex impedance of its magnitude and phase angle but only for certain frequencies but anyway through the impedance concepts we could now not only calculate the current voltage and phase values for such a simple circuits but more complex ones as well but then again you would need to be familiar with a bit more complicated math which was definitely not the point of this video the point was for me to show you that when it comes to AC circuits the combination of inductance resistance and capacitance changes the magnitude of the current in its face which can offer challenges for electronic designs but due to the concept of impedance it is something we can easily understand and calculate and with that being said I hope you learned something new through this video if so don't forget to like share and subscribe stay creative and I will see you next time

Channel: GreatScott!

Views: 195,720

Rating: 4.9404979 out of 5

Keywords: impedance, ac, AC, inductor, coil, capacitor, resistor, R L C, resistance, reactance, ohmic, explain, basic, basics, guide, beginner, beginners, tutorial, experiment, capacitance, capacitive, inductive, inductance, calculate, calculation, current, voltage, phase, angle, shift, complex, number, imaginary, real, plot, draw, plane, reactive, power, apparent, compensation, trigonometry, electronic, electronics, greatscott, greatscott!

Id: W2VwAL7-8-o

Length: 10min 9sec (609 seconds)

Published: Sun Oct 21 2018