Timeline for Current - Voltage curve for non-ohmic material
Current License: CC BY-SA 3.0
26 events
| when toggle format | what | by | license | comment | |
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| Jun 14, 2015 at 18:49 | vote | accept | GPerez | ||
| Jun 14, 2015 at 18:37 | comment | added | DanielSank | By the way, see this meta post where the most upvoted answer supports that explicitly indicating your study level is not appropriate. | |
| Jun 14, 2015 at 18:30 | comment | added | GPerez | @CuriousOne Of course this is the only thing the lab asks. As I say this is for "further reading" and for my own curiosity. And at this point I am quite reconciled with the idea of no analytic solution! | |
| Jun 14, 2015 at 18:30 | comment | added | DanielSank | Is there some way to start a chat room with you? | |
| Jun 14, 2015 at 18:28 | comment | added | CuriousOne | @DanielSank: Cool... makes me want to ask what you are processing. Please, pretty please? :-) | |
| Jun 14, 2015 at 18:26 | comment | added | DanielSank | @CuriousOne Not sure. Too busy trying to solve a signal processing problem... | |
| Jun 14, 2015 at 18:24 | comment | added | CuriousOne | @DanielSank: looks like you got it covered. The equation doesn't look like it's analytically solvable, though, is it? :-( | |
| Jun 14, 2015 at 18:22 | comment | added | DanielSank | I wrote an answer, which coming back to the comments looks a lot like what @CuriousOne had in mind. CuriousOne, if you want to edit for clarity/content please go for it. | |
| Jun 14, 2015 at 18:20 | comment | added | CuriousOne | My feeling is that all the lab asks for is a discussion of the non-linear structure of the measured voltage-current relationship without a microscopic theory. If you wanted to model this to, I would guestimate, a few percent accuracy, using Stefan-Boltzmann should work. The problem is that the resulting equation probably doesn't have an analytic solution, since Stefan-Boltzmann will introduce a fourth power in $T$. Please note that $T$ in this case is absolute temperature in Kelvin and that one has to use a radiation balance i.e. there is a term for the radiation absorbed from the environment. | |
| Jun 14, 2015 at 18:20 | answer | added | DanielSank | timeline score: 3 | |
| Jun 14, 2015 at 18:10 | comment | added | GPerez | @CuriousOne (...) If you answer with what Stefan-Boltzmann would more or less look like in my case I'll be glad to accept. | |
| Jun 14, 2015 at 18:09 | comment | added | GPerez | @CuriousOne The lab instructions don't really ask for any of this. They just have to plot the data and say "yup, not linear". Certainly they have no knowledge of Stefan-Boltzmann! Still I'd like to find the models that describe the situation and give a decent explanation for the shape of the curve. The lab report is complete as is, at this point this is for understanding's sake (which sadly isn't provided by many high-school assignments). Also I have become interested in the matter myself and would like some closure! (...) | |
| Jun 14, 2015 at 17:53 | comment | added | CuriousOne | The hint "lightbulb" would suggest that you are looking at a system that is reasonably close to a black body radiator. The radiated power as a function of temperature would be given by the Stefan-Boltzmann law: en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law. Having said that... I am not entirely sure that this is really what they are asking for in this lab. Do you have the original lab instructions? | |
| Jun 14, 2015 at 17:43 | comment | added | GPerez | @CuriousOne Thank you, I was hoping to arrive at something like this. I have no idea so you may choose the simplest model. If it is black body so be it! Can you let me know so I can edit it in? | |
| Jun 14, 2015 at 17:39 | comment | added | CuriousOne | The dissipated power is simply $P=V^2/R$ but there is no way that you can estimate the temperature as a function of the dissipated power - that's system dependent. It's different for an ideal black body than it is for a grey body (not it becomes a non-trivial function of the body's spectral properties) and it's different, again, for an air cooled resistor. Unless you can tell us what your model assumptions are (I suppose it's black body radiation), we can't help you. | |
| Jun 14, 2015 at 17:38 | history | edited | GPerez | CC BY-SA 3.0 |
edited title
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| Jun 14, 2015 at 17:37 | comment | added | DanielSank | $I$ is "current" not "intensity". | |
| Jun 14, 2015 at 17:27 | comment | added | GPerez | @DanielSank I wrote $P = f(T)$ mainly by a vauge recollection that temperature is some mean of "energy". Also if it were true I could exploit it to relate my "variable resitance" model (1st. eq) to Ohm's law. If it's not true, I need some other way of relating the two, don't I? What relation does temperature have to voltage and intensity, independent of my first equation? | |
| Jun 14, 2015 at 17:22 | history | edited | GPerez | CC BY-SA 3.0 |
deleted 1 character in body
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| Jun 14, 2015 at 17:20 | comment | added | GPerez | @DanielSank In my opinion one such sentence isn't distracting. But let us not argue over such a triviality. As for total change in temperature, I'm pretty much reading off a lazy lab sheet description where $\Delta T$ is written. I assume that there is a $T_0$ where the resistance is exactly $R_0$, and $\Delta T$ is the offset from $T_0$. Now that I think of it I shall edit accordingly. | |
| Jun 14, 2015 at 17:04 | comment | added | DanielSank | When you say $T$ is the "total change in temperature" do you just mean that it is the temperature (in a sane unit system like Kelvin, i.e. no offset from zero)? Also, the equation $P=f(T)$ seems wrong. The energy dissipated by an electrical circuit ($P=IV$) is usually equal to the generated heat power but that's not necessarily the same as the change in the circuit's own temperature. | |
| Jun 14, 2015 at 17:02 | comment | added | DanielSank | Of course context helps, but the style of the site favors objective questions with objective answers. As such I generally think that the question itself dictates the appropriate level of the answers. Therefore, explicit statements about the question's author's background tend to be more distracting than helpful. | |
| Jun 14, 2015 at 17:00 | history | rollback | GPerez |
Rollback to Revision 1
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| Jun 14, 2015 at 17:00 | comment | added | GPerez | @DanielSank Not irrelevant. SE questions are best answered with as much context given as possible, within reason. I think that one sentence is within reason. | |
| Jun 14, 2015 at 16:52 | history | edited | DanielSank | CC BY-SA 3.0 |
Removed irrelevant comment about OP's ignorance
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| Jun 14, 2015 at 16:45 | history | asked | GPerez | CC BY-SA 3.0 |