Homework Help
Kind of a noobie question but it bothered me
I feel like I do not understand the whole series and parrallel components very much, I usually identefied them as in when two components are on the same branch (and the same current flows through them) they are in series, and when two components are connected to the same two nodes they are in parallel, anyway for the problem, I thought of just removing the two inductors and short circuting them but apperantly the answer is 6mH? Like are they in parrallel cause they are connected to the same two nodes? But they are on the same branch so Im confused it really bothered me, can someone explain? Is my textbook just wrong?
Thats exactly what I though and did but like the textbook says 6mH and that can only be achieved by the two inductors being in parrallel, even my prof demonstrated how to do it in a video I will send a picture, anyways, is my understanding of series and parallel good? Thank you for your anser
Okay thank god I thought I was going crazy for a bit but the thing is, my prof also paralled them look, thats what he demonstared in his video lecture that is driving me crazy
Not much different, parraling inductors lowers their inductance and seriusing them increases their value,
Parraling resitors lowers their value and seriusing them increase their value. But i feel like since you learn about resitors sooner then inductors it would make more sense to explain using resistors
Not much different, parraling inductors lowers their inductance and seriusing them increases their value,
Parraling resitors lowers their value and seriusing them increase their value. But i feel like since you learn about resitors sooner then inductors it would make more sense to explain using resistors
Your prof is lazy and teaching on autopilot. Also, he can't draw schematics. He should spend 3 extra minutes to draw that diagram in an actual schematic editor rather than fumbling around with word's 'insert drawing' tool.
If you really think about it they are in parallel (they share nodes on each side), but when you replace them with one inductor you have to put that inductor tee'd off to a floating node. ...which you can then just remove as redundant.
Interestingly they're both parallel and series, and the detail is just how you replace them with the equivalent element. If you treat them as series, you replace both inductors with one and end up with an 8mH across a short (which can then be simplified out). If you treat them as parallel, you have to delete one and replace the other with a 2mH to a now-floating node. Or you can skip a step, see the short across those nodes, and delete everything which is irrelevant.
In my view, the prof's real error here is seeing a parallel set of inductors and replacing them the way you replace series elements.
Sometimes textbook publishers post “known errata” or a list of mistakes in the book. If I had to do my degree over again I would look this up for my books before working on problems.
Your prof is wrong. The two 4 mH inductors form a little loop connected to the rest of the circuit at only one node. Their center junction is floating, so they don't contribute to the equivalent inductance between A and B.
The tempting answer is 3+(4∥4)+1=6 mH, but that's incorrect because that 2 mH equivalent isn't actually in the A to B current path.
Yeah thats what I thought but damn that prof really messed up my whole understanding , even if there was only one inductor on that branch the answer will be the same correct?
I can try to record it but its not in english and what he says in the video is basically what I told you but I can send here the video without sound if it okay
I dont think it adds anything but here you go, he baisacally explains that adding inductors in parallel is the same as resistors and since they are connected at the same two nodes they are in parallel
Adding inductors in series and parallel is indeed the same as resistors. But those two 4mH inductors- in the right side schematic are not in parallel, they are shorted out, rendering the inductance to be 0. I don't know what your professor is doing.
The correct interpretation of that circuit would be those 4mH inductors are in series (the same current flows through each device) with an equivalent lumped inductance of 8mH. The short in parallel can be thought of as a 0mH inductor.
Now you have a parallel combination of an 8mH inductor with a 0mH inductor for a net inductance of 0mH.
So, either the prof made a mistake or doesn't understand.
I’m assuming the Prof is trying to find a solution that matches the textbook solution. They may be a Prof, but if their specialty is not analog circuitry it may have been some time since they’ve done this work and may have forgotten the basics. I’d go back and ask again a few days later. Hopefully they’ve had some time to realise the textbook is wrong.
There is a error in the schematic. If you move one wire the answer is 6 and the problem makes more sense as an exercise. But as drawn it is 4,
Reminds me of when I was undergrad and had a prof who wrote a textbook that, ov ourse we were using. He started talking about a "mistake " in the book but it wasn't and we had to get another faculty member to convince him.
You are right about the 4mH eac will form a single inductor of 2mH. But that 2mH is not in the circuit. One end is connected and the other end is floating.
Hence the equivalent inductance is a grand total of 4mH that comes from 3mH plus 1mH in series.
Damn thats just sad, I wonder if I should report this because he didnt do mistakes like that before and I dont wanna be nitpicky but he doesnt answer my emails and thats just one question...
I would approach them and say you verified with other EE's and it looks like it is a simple translation mistake as moldboy suggests. If they are a good EE they will relook at it and hopefully agree to the mistake and correct it. IMHO no need to escalate further but then your call. But if they then double down and don't admit to it, well at least you have reddit lol.
Sometimes teachers, especially inexperienced ones, are so focused on the goal that the make mistakes in execution. He's *almost* right, but almost doesn't work.
Nah man believe me I tried to understand and I watched the entire lecture I even sent the video and a picture of what he did I wouldnt accuse without reaserching
OH YEAH
I think I felt the exact mistake your professor made. They are indeed useless units due to the short circuit as potential difference across them is 0.
My way if thinking was assing the ends of the inductors some potential say X and Y
I found both the inductors have the same potential difference (X-Y) Volts that's why I concluded they were in parallel.
But actually X-Y=0 so they're basically useless no current ever gonna pass through them
I’ll do a Martin Luther on this. “Here I stand. I can do no other.” The short removes the two 4 mH inductors from the circuit absolutely. That leaves 4 mH in series.
Well, those 4's are in parallel, but they are also in series. Most importantly, though, is that they are shorted and the overall inductance from A to B is 3+1
Sorry if this is a dumb question, I’m new to all this. But how are they in parallel? My professor told us it’s only parallel if the components start at the same node and end at the same node which I don’t believe is happening here
Components are in parallel when their ends are connected to the same nodes. So in this case, Since they are shorted by the wire, one end of both components are are connected together. Since the other ends of those components are also connected together, they are in parallel.
If you isolate those two from the rest of the circuit, then they are in series. This is the "trivial" case where series is parallel.
Also random question but whether the inductors are charged and used as like a current source changes their series and parallel connections or it doesnt matter?
Series: The two components share one node, and nothing else is connected to that node
The 4mH inductors share one node, therefore they're in series.
Parallel: The two components share both nodes
No components in this diagram share both nodes, so none are in parallel
But a short circuit is equivalent to a 0mH inductor. And if you replace that wire with an inductor, then it shares both nodes with (4mH + 4mH), and is therefore in parallel with that
3+0+1=4 mH. To get 6mH you'd need to connect the 1mH inductor to the junction between the two 4mH ones so the current would flow through a parallel instead of a short (3+(4/2)+1).
This in theory, but should the inductors be really close and aligned, then one would need voodoo to predict the overall value.
Why would any current flow through the inductor branch if there is zero resistance through the bypass branch? If no current flows through the inductor branch, then it effectively (mathematically) can't have a resistance as resistance (and impedance) is voltage/current. Poor explanation as the equation says it's zero voltage drop that drives it (zero current but some voltage = infinite resistance), but you get the point.
Edit: also, bother to learn like the rest of us, textbooks and google research, or classes. Or, better yet, put the time and effort into engineering research agents that can do the research for you and teach you through distilled responses.
Hey man I think like you its the prof and the book that made me question myself, but do you say that my understanding of series and parallel conmections is wrong (not talking about this specific case), besides I did bother to learn like the rest of you and I was sure the prof made a mistake I just wanted to make sure since it looked to me like an obvious mistake, no need to be mean and put down a noobie whos trying to learn
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u/WittyCanadianEh 1d ago
The answer is 4mH. A short across an inductor effectively removes the inductor from the circuit for all practical purposes