Unraveling the Mystery of Phase Differences in Passive Circuits

[I_am_learning]

IssacBinary, you are indeed very strange. I myself, avoid trying to visuallize and follow step by step instants on the cycle. I understand it like this: "when I make this and this arrangements, and apply sinusoidal force here, some crazy things must happen". I then use maths to find out what will happen (instead of trying to analyze like you). After the solution is found, I try to visualize what the solution look like. I find it plausible and say, 'That looks ok. let's move on'.
However, I was at beginning, I was also like you, trying to gain insights by analyzing every moment. But given so many things to learn and so many arrangements and complexities we need to deal with, its not always possible.
For eg, if I draw out some another similar similar circuit with few more capacitors and inductors, and if you try to visualize the oscillation involved there in a way you are trying to do here, then you may burst your brain. :)

 

[Bassalisk]

I got a magic answer, that i personally learned over the past year. Its universal.

"You don't have to visualize everything to understand it". Phase is one of those things. If you can use it calculations, what's the point? Math is always there to back-up everything.

 

[NascentOxygen]

I got a magic answer, that i personally learned over the past year. Its universal.

"You don't have to visualize everything to understand it".

If you say that works for you, then I'll take your word for it. But I sure would not recommend that others subscribe to that notion.

Phase is one of those things.

Phase is so easy to visualise, and to illustrate, that I can't see why anyone would want to
evade doing so. It can only help understanding. Visualisation takes the mystery out of many concepts, and aids design and troubleshooting.

Wasn't it Tesla, the greatest electrical engineer ever, who designed his motor in his mind. When someone asked would he be building one so he could test it, he replied there was no need, he had already run the tests on it in his mind.

If you can use it calculations, what's the point? Math is always there to back-up everything.

Maths is not a whitewash for a meagre understanding.

 

[Bassalisk]

If you say that works for you, then I'll take your word for it. But I sure would not recommend that others subscribe to that notion.
Phase is so easy to visualise, and to illustrate, that I can't see why anyone would want to
evade doing so. It can only help understanding. Visualisation takes the mystery out of many concepts, and aids design and troubleshooting.

Wasn't it Tesla, the greatest electrical engineer ever, who designed his motor in his mind. When someone asked would he be building one so he could test it, he replied there was no need, he had already run the tests on it in his mind. Maths is not a whitewash for a meagre understanding.

Understanding mathematically what is happening can be enough for me. Yes Tesla did run tests in his mind, but in my opinion he was an innovator not a scientist, he didn't bother too much with formulas. Maxwell was a scientist and he had greater power of understanding by having very good math. This is solely my opinion and I am first year EE. This is my comprehension of my current knowledge of EE.

I am only for understanding everything physically. But I can't sometimes and math gives me good bedding.

 

[f95toli]

Phase is so easy to visualise, and to illustrate, that I can't see why anyone would want to
evade doing so.

Phase is not always easy to visualize. I did my PhD working on current phase relationships in high-Tc superconductors. In these materials the phase shift depends on the direction the current in flowing with respect to the crystal axes (due to the d-wave symmetry of the pairing wavefunction); the microscopic theory for this is very complicated. Moreover, one of the things I measured was the quantum mechanical tunnelling of the phase. At low enough temperatures the phase of a electrical circuit can become quantized, meaning it can go from one value to another via tunnelling (phase is actually the conjugate variable to charge); this is once again a good demonstration that phase is a much "deeper" concept than most people realize (meaning there is more to phase than just time-differences if that is what you were referring to).

Hence, yes there are situations where one CAN "visualize" the phase. But this is not true in general, and relying to much on "visual" pictures and analogies for phase and similar things can become a serious problem later on when you study more advanced physics (very few things in for example quantum mechanics can be visualized, or even understood in the conventional meaning of the word). It is therefore important that you get used to understanding things at an "abstract" level early on, you need to be able to "think" math.

 

[Studiot]

Phase is not always easy to visualize....

Funny that, I was going to reply with a similar comment but stopped for a cup of tea and there was your post when I came back.

I was just starting to prepare a qm response for another thread and saw and saw this.

If your function is say

$$\Psi = {\Psi _0}\exp \left( {\frac{{i(xp - Et)}}{\hbar }} \right)$$

I definitely find phase less than easy to visualise directly.

go well

 

[sophiecentaur]

Wasn't it Tesla, the greatest electrical engineer ever, who designed his motor in his mind. When someone asked would he be building one so he could test it, he replied there was no need, he had already run the tests on it in his mind.

I have to take issue with that (tongue-in-cheek?) description of good old Nicola. An Engineer is someone who actually implements a viable version of what an Inventor may produce in the form of a prototype or a description. He was a great Character, no doubt but the rest is far too much of a myth for me to take seriously. Distance lends enchantment, I think.

 

[NascentOxygen]

Phase is not always easy to visualize.

Phase is easy to visualize in the topic of this thread, viz., the phase shift in a 1st order passive circuit. :uhh: We are not even onto 2nd order circuits, yet.

The distraction of fluid friction and crank shafts was, I thought, bad enough. Now we have quantum physics wanting to poke its nose in. No wonder the OP is still apprehensive about his shaky understanding after nearly 100 posts on (and off) the topic.

If he can't grasp the simplicities of phase differences in passive circuits, he will stand no hope when he progresses to more complex circuits.

The challenge is not to complicate the scenario to such an extent that the learner has no chance of understanding it. That's easily done. (As you very capably demonstrated)

The OPs best interests are served by placing yourself where he is, and progressing in measured steps from there. Phase shift is easy to visualize, and OP has been able to do that right from the start. The whole thread (yes, there is supposed to be a common thread somewhere in here) came about because he wants to know how, in an R-C circuit, a phase intermediate between 0 and Pi/4 comes about. Quantum phenomena, as interesting a distraction as they may be, have nothing to do with it.

 

[NascentOxygen]

I have to take issue with that (tongue-in-cheek?) description of good old Nicola. An Engineer is someone who actually implements a viable version of what an Inventor may produce in the form of a prototype or a description. He was a great Character, no doubt but the rest is far too much of a myth for me to take seriously. Distance lends enchantment, I think.

Tesla does have a reputation of being a bit of a showman, but I wasn't referring to that. He was both inventor and engineer. Holding a patent on the invention of the induction motor firmly earns him his place in the halls of engineering, quite apart from all his other works. While he is mostly remembered for his work with alternating current, but wasn't it Tesla who discovered a way to generate ball electricity--and store it? No one has been able to replicate that feat. Eccentric, sure, but still with all the traits of the quintessential engineer in my books.

The only black mark I care to place against Nikola Tesla is that he took the secrets of some of his inventions to his grave. But given the way he was not appreciated in his time, who can blame him?

 

[f95toli]

Phase is easy to visualize in the topic of this thread, viz., the phase shift in a 1st order passive circuit. :uhh: We are not even onto 2nd order circuits, yet.

So what? The question was "Physically, what is phase?". And the OP has already stated that he/she does not accept a mathematical description. Hence, one must then assume that what is needed is some sort of physical model of what is "really" going on. What I am saying that the concept of phase is actually quite complicated. Note that in all of the examples I mentioned above I was referring to real electrical circuits (chips), circuits that are modeled using LCR circuits and where the phase is measured using oscilloscopes etc.

The only reason I brought up superconductors is that it is a nice example; there are many more "mundane" examples where dealing with phase shifts can become even more complex, such as ferrite components (used in high frequency circuits). Even if there was a simple explanation for what is being asked, I don't think I would necessarily give it; simply because that would make it even more confusing when dealing with more complex problems (even in fairly trivial cases such as understanding the physics of an inductor or non-linear components) .

If he can't grasp the simplicities of phase differences in passive circuits, he will stand no hope when he progresses to more complex circuits.

Agreed,

The OPs best interests are served by placing yourself where he is, and progressing in measured steps from there. Phase shift is easy to visualize, and OP has been able to do that right from the start. The whole thread (yes, there is supposed to be a common thread somewhere in here) came about because he wants to know how, in an R-C circuit, a phase intermediate between 0 and Pi/4 comes about. Quantum phenomena, as interesting a distraction as they may be, have nothing to do with it.

I have been where the OP is. But I got over it.
The problem is -as we keep coming back to- is that the kind of non-mathematical "understanding" that the OP is asking for does not necessarily exist; sooner of later (and the sooner the better) one reaches a point where one has to learn to "think" math, where understanding the model and the math means that one has understood the problem fully.

 

[DrClapeyron]

I have always thought about phase as being a periodic change in voltage, and thought about electrical components in a circuits as a way to produce a voltage pattern to send signals.

I think of AC current like this: for the standard American house hold outlet you get 120v of electricity 60 times every second or 60 Hz. Extending that to a three phase power distribution system, you have three phases, one on each conductor, which connect to a motor or single transformer that when they arrive act like one phase. Almost as if they were staggered like Olympic sprinter starting points, where you have to take into account a runners distance from the inside of the track.

Therefore I have always thought of phase as a package of varying voltages. I have no idea if this is correct but I can not help being curious.

 

[NascentOxygen]

Generally speaking, a working concept of any phenomenon need be no more complex than is necessary to adequately serve your needs.

I think of AC current like this: for the standard American house hold outlet you get 120v of electricity 60 times every second or 60 Hz.

There is nothing wrong with what you write. But it would be even more correct to say that you get up to 169v of electricity so many times every second. Remember that 120v is the RMS value of the sinusoid. Your 120v supply smoothly swings from -170v to +170v every cycle. (120 x sqrt 2 = 169.7)

While I can see why you wrote "60 times every second" you could equally have said 240 times every second.

 

[NascentOxygen]

So what? The question was "Physically, what is phase?".

No. That's the subject header. For the question you have to read the message that comes under that header. (I sharn't repeat it here, because in his second post, OP further defines and refines his question.)

And the OP has already stated that he/she does not accept a mathematical description.

Sorry?? "Does not accept" you say?

Let's take a look...

I understand them mathematically

Difficult to see any refusal of a mathematical representation there!

What I am saying that the concept of phase is actually quite complicated.

The concept of phase difference in a linear passive circuit (which is what is under discussion here) is only as complicated as you wish to make it.

I fear that the OP has long ago abandoned reading this derailed thread. But just in case IssacBinary is still soldiering on (in the vain hope of a modicum of enlightenment), I hope that somewhere in this miasma you have been moved a little farther along the path to understanding the genesis of phase differences in a first order R-C system. I believe I can, belatedly, see exactly what you were hoping to have explained. But this thread has staggered on for too long, and I'll leave it until the question arises at another time, to write around the explanation sought.