Does the imaginary part of the voltage in an RLC circuit really exist, or is it just an artifact of the math we use to derive it that can be discarded? Is there any way to measure it? |
- Does the imaginary part of the voltage in an RLC circuit really exist, or is it just an artifact of the math we use to derive it that can be discarded? Is there any way to measure it?
- What material could produce the X-ray florescence spectra for this historical artifact?
- What causes the distinct "chopping" sound of a helicopter if the rotation of the blades is constant?
- Do atoms emit spectral lines in the nonvisible spectrum?
- How does propulsion in space work?
- If I were to put a capacitor in a microwave oven, would it be charged by current induced by the microwaves?
- Has there ever been a mathematical conjecture that appeared true due to Heuristic justification but eventually was shown to be the opposite by a far outlying counterexample?
- Why don't spacecrafts use nuclear fuel?
- How does tritium glow?
- Is the sequential atrial contraction simultaneous with the contraction of the ventricles? Or is the ventricle contraction delayed by a moment?
- Why can't we see stars in pictures taken from the moon?
- Where do scientists obtain radioactive isotopes of common elements such as Oxygen and Carbon for experiments that involve tracking the movement of molecules?
- If we can calculate/know the speed and direction of particles in the universe, couldn't we theoretically know the future? What is the counter argument for a deterministic view of the universe?
- On the topic of light pressure and flashlights, how long would it take for a flashlight turned on in the vacuum of space to propel itself to the speed of light?
- Does the movement of astronauts effect the trajectory of their vehicle?
- Is FTL communication possible if morse code and Quantum Entanglement are used?
| Posted: 12 Oct 2016 06:59 PM PDT So in my physics class that I took last semester we learned about RLC circuits and my teacher sort of handwaved away the imaginary part of the voltage, saying "we only care about the real part." Is this totally true or is there just a deeper rabbit hole he didn't want to get into for the purposes of our class? If we have a capacitor, resistor, and inductor in series and in a closed loop with no external voltage source (for the purposes of this explanation, anyways.) We can use kirchoff's law to derive the fact that the voltage drop over any closed loop is zero, so we get:
-L(dI/dt)-IR-(R/C)=0
=-L(d2 Q/dt2 )-R(dQ/dt)-(Q/C)=0
=(d2 Q/dt2 )+(R/L)(dQ/dt)+(1/LC)Q=0
So now we have a differential equation, whose solution we can guess is something like : Q=Aeiωt
Therefore:
-ω2 Aeiωt +iω(R/L)Aeiωt -(1/LC)Aeiωt =0
=-ω2 +iω(R/L)-(1/LC)=0
Where (1/LC) is some resonant frequency ω0 squared, so we can solve the quadratic:
-ω2 +iω(R/L)-ω02 =0
to find ω, which will be:
ω=i(R/L)±sqrt(ω02 -(R2 /4L2 ))
[edit: i skipped some parts here, i'm just going off what i have in my notebook]
so finally Q=Ae(-R/2L)t +iωt
which is e to a complex power, which can be re-written using euler's formula, which gives a real and an imaginary part:
Q=Ae(-R/2L)t cos(ωt)+Ae(-R/2L)t isin(ωt)
so now for Q we have a real and imaginary part. So what does the imaginary part mean in reality? If we tried to see it on an oscilliscope, per se, could we? Could we have some sort of device that would measure charge or voltage in the complex plane? Or does none of this matter because the imaginary part is just an artifact of the mathematics that doesn't have any real meaning?
thanks for your time, anyone who reads and is able to respond to this. [link] [comments]  |
| What material could produce the X-ray florescence spectra for this historical artifact? Posted: 12 Oct 2016 08:46 AM PDT Hi there, Science! I'm a historian doing archaeology, which means I'm doubly out of my element (so to speak). I've been looking at glass beads that were dropped in the outhouse of a New England boarding school sometime in the 1860s. Most of them are simple glass beads, perhaps used for teaching girls crafts, but I've got one that I can't identify. It's definitely not glass, but I also doubt it's jet, which was sometimes used for fancier things. Because it's a historical artifact, any form of destructive analysis is out of the question. I used an X-ray florescence tracer at two different settings, one that excites only low-Z elements (generally those less than Zn) and one that excites high-Z elements and uses a filter to absorb excess energy and obscure X-rays returning from low-Z elements. For those not in-the-know, X-ray florescence sends X-rays into an object, which excites the electrons; when they settle back down, they produce X-rays of their own depending on how big their home atoms are; the tracer collects these return X-rays and plots how many arrive at each energy level, basically producing a chart of which elements are present in the object. As you can see, the low-Z spectrum reveals almost no Si, which is the predominant element in glass. It instead spikes at S and Ti, with a number of other trace elements as well. The spike at Rh/Pd is caused by the X-ray tracer itself and can be ignored (although it obscures any Cl that might be present). Note that the tracer also has a hard time picking up elements beneath Al, so I can't assume that C, O, or other light elements are absent. Regarding the high-Z spectrum, the peaks at Rh and Pd can again be ignored, and the broad peak around 19.0 keV is the Compton peak representing a scattering of the Rh/Pd energy; it's height suggests that this isn't a very dense material, but it doesn't tell us much more. There are small peaks for most elements between Ti and Zr, with taller peaks at Ti and the Sr-Y-Zr combo which suggests (to me) a natural mineral source. This is all qualitative kind of stuff, and unfortunately, there's no way to translate this data for rigorous quantitative analysis (unless I did destructive analysis on a small sample, which is again out of the question). I did push it through a program called PyMca, which uses fundamental parameters (i.e. a large number of assumptions that never quite match reality), and I almost certainly made errors in using the program. These data should be taken with a high degree of caution. Nevertheless, here's the elements that PyMca calculated having a mass fraction of ≥ 0.5% in each spectrum. Low-Z: Si 1.27%, P 0.50%, S 10.27% (Ti came out surprisingly low). High-Z: Se 2.97% (whereas I would have expected Ti, Sr, and Zr, with possibly Fe, Ni, Cu, Zn, Hg, Y, and Sn as well). My next step is using PyMca (or some other form of analysis) to produce more believable mass ratio data. So that's what I've got! Does anyone have thoughts on what this could be, good places to find reference data that I can compare spectra or calculated mass ratios to, or any other constructive ways to use the data on hand? I'm grateful for any ways out of this dead end (but keeping in mind that I have only little access to the artifact and absolutely no access to research funds). EDIT. Thank you for your overwhelming interest and knowledge! I've gotten a lot of great recommendations for future methods of analysis—Raman spectroscopy, infrared spectroscopy, energy dispersive x-ray spectroscopy, etc.—but for the moment I'm constrained to what I've got. The general consensus seems to be that the base matrix is probably rubber (organic, comprised of light elements that don't show up with X-ray florescence) hardened or "vulcanized" with Sulfur. Charles Goodyear patented this process in 1844, and the hardened rubber, also called Ebonite, was soon being sold as a cheap substitute for fancy jet jewelry. This bead could very plausibly be a cheap bit of jewelry, perhaps even a bolo tie, although I've also gotten a few other interesting suggestions: an early electrical part, a jacket button, or even a piece for a stringed instrument. The Titanium peak may represent Titanium Dioxide, which can be used to opacify and whiten a material. In this case, that would probably be a white paint or other residue, which may be seen in the grooves on top. I suspect that this might come from lead paint that was dumped or otherwise leached into the outhouse on top of the bead. Although surface contaminants didn't substantially affect my assays of glass beads, in this case it may have been different. There was no white residue visibly present where I took my assays, but it may have bonded or otherwise permeated the surface and thus contaminated my results. With these things in mind, I'd appreciate any further thoughts:
[link] [comments]  |
| What causes the distinct "chopping" sound of a helicopter if the rotation of the blades is constant? Posted: 12 Oct 2016 07:49 PM PDT |
| Do atoms emit spectral lines in the nonvisible spectrum? Posted: 12 Oct 2016 06:39 PM PDT I'm taking a Stellar Astronomy course, and have a very limited understanding of spectroscopy. My basic understanding is that emission lines are the result of electrons needing a very specific amount of energy before they can change orbitals, and when changing orbitals they emit a photon to account for the energy change. This photon results in the emission line, right? Assuming I have that understood properly, Here is my question. Do atoms have emission/absorption lines in the radio/infrared/ultraviolet etc. spectra? And if so, could we gain any information by examining these additional spectra? Like I said, My understanding is very limited, but I really enjoy this subject and look forward to the answer! [link] [comments]  |
| How does propulsion in space work? Posted: 12 Oct 2016 09:45 PM PDT I know that space is for the most part a vacuum. So considering newton's third law, if space shuttle (or any object) is at rest its pretty much stuck there, and ay the same time its trajectory is pretty much set once it 'leaves' a large body's gravitational field. [link] [comments]  |
| Posted: 12 Oct 2016 07:14 PM PDT In addition, would an LED light up in a microwave? Or would both the LED and capacitor just spark and overheat? [link] [comments]  |
| Posted: 12 Oct 2016 06:13 PM PDT The Goldbach Conjecture appears to be true from heuristic justification alone since it has been tested to such an extremely high value, but without a concrete proof, there could always be a number that doesn't work (which would disprove the conjecture). Heuristics is also an argument used for the Collatz Conjecture being true -- but has there ever been a mathematical conjecture that appeared true for some time but was proven false by an outlier? [link] [comments]  |
| Why don't spacecrafts use nuclear fuel? Posted: 12 Oct 2016 06:57 PM PDT |
| Posted: 12 Oct 2016 05:57 PM PDT Tritium as i understand it, is an isotope that is radioactive, unstable, and luminesces even without external energy. How does this work, what colors can it glow in, and how long will it be able to glow for beforr deteriorating? [link] [comments]  |
| Posted: 12 Oct 2016 07:59 PM PDT |
| Why can't we see stars in pictures taken from the moon? Posted: 12 Oct 2016 06:27 PM PDT I saw a couple pictures recently (at separate times from seperate posts) taken on the moon, with the "sky" in the background. One was a picture of Earth (seen on today's front page.) You could see no stars, and I'm curious as to why! [link] [comments]  |
| Posted: 12 Oct 2016 01:02 PM PDT I thought about this after reading in my textbook about the procedure that Melvin Calvin and his colleagues used to identify the carbon compounds created in photosynthesis. How does one "make" radioactive isotope? Or, are they just collected as natural radioactive isotopes that are sorted and stored for such purposes? [link] [comments]  |
| Posted: 12 Oct 2016 12:30 PM PDT This plays into whether we actually have any willpower (i.e. can actually make choices). I know one theory is that quantum events in our brains could be the source of our (potentially perceived) willpower, but to me it still seems possible for choice to remain just an illusion. I know this may count as a philosophy question as well, but I'd love to hear the science side first. [link] [comments]  |
| Posted: 12 Oct 2016 10:06 AM PDT For simplicity's sake assume the flashlight has a super powerful battery that lasts eons. [link] [comments]  |
| Does the movement of astronauts effect the trajectory of their vehicle? Posted: 12 Oct 2016 11:42 AM PDT I've seen them using the bulkheads to kick off of to move around inside. Does this effect their trajectory moving through space or are they moving fast enough that they don't need to account for the force? [link] [comments]  |
| Is FTL communication possible if morse code and Quantum Entanglement are used? Posted: 12 Oct 2016 08:33 AM PDT Context: A friend and I were talking about Quantum entanglement. somewhere in the conversation, he mentioned that information can be sent instantly. I said no useful information can be sent. Then we talked about useful information could be encoded and sent, but the decoding algorithm would at most travel at the speed of light. This got me thinking if a far off place also knew of the morse code, I could sent dots and dashes through instantly, which can be decoded properly. Now, this means that I sent across useful information across. This violates the no useful info can go ftl law. Am I missing something? [link] [comments]  |
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