Jump to content

Danijel Gorupec

Senior Members
  • Posts

    694
  • Joined

  • Last visited

  • Days Won

    2

Everything posted by Danijel Gorupec

  1. If anyone interested... I went to a store and bought a torch - spent more than I expected (cca 70EUR; 75USD - one fuel bottle included). I took the most powerful torch of this type they had. It proved very capable, so maybe I could choose a cheaper one. They call the fuel the "MAPP gas". I understand this is some propylene - butane mixture. Hotter than butane, they say. So, I filled a shallow steel pot with dried crushed stones (angular rock 5-10mm), because I didn't have anything better. Placed steel pieces onto the rock and heated it with the torch. Btw, while heating, the surrounding rock also becomes red-hot (at surface). Interestingly, some gray (granite-like color) rock pieces turned white after this heat treatment. I kept the metal dark-red-hot for about one minute, and then using pliers transferred it into different pot full of wood-ash (I didn't have anything else, but I read that wood-ash is a good choice). Buried inside the ash the metal cooled slowly enough, I hope. I annealed following items: a small nail, M5 screw with a nut, a short bright-drawn steel rod, few pieces of transformer lamination (silicon steel) Results: To check if I am doing anything good, I compared the annealed nail (sample A1) with an identical non-annealed nail (sample A2). I was surprised how much easier it is to bend the annealed nail. I could bend it with fingers (the smaller bend on the A1 sample is done with fingers only; the larger bends on both samples are made with a help of a vise). Must be I am doing something right. To check dimensional stability, I annealed a screw with a nut on it (sample D). Unwisely, I choose a coated screw (a bright coating - is this nickel or what?). This coating turned green during heat treatment, so it was less easy to monitor the temperature of the sample. The nut, being smaller, become dark-red-hot much faster than the screw (obviously, there was not that much heat transfer between the nut and the screw).... After the cooling, it was equally easy to turn the nut as before annealing - so I suppose, the dimensional stability is good enough. The nut did not weld itself to the screw. The bright-drawn mild-steel bar sample (B1) - fi 8mm x 36mm - turned dark (after cooling). It looked more like a hot-drawn or hot-rolled steel. You can see it in comparison with the non-annealed sample B2. Electrical steel lamination (sample C1) has large surface - so I was afraid it might cool to fast. The sample C2 is not annealed. Not much difference between the two. Magnetic measurements: I broke the core of a small transformer (old one, low-quality one - there is no insulation between lamination layers) - I arranged it so that I can place metal samples to close magnetic circuit. Look at the picture: the sample B2 is placed into the measurement position (I would also place a weight of non-magnetic material onto the sample during actual measurement). I am pushing sine-wave current, of constant amplitude, into one coil and then measuring voltage in the other coil. The setup has very bad sensitivity because there is large magnetic reluctance in the gap between sample and transformer core (I guess, larger than the reluctance of the sample itself). Therefore I couldn't measure anything precisely. The results I obtained, are not entirely clear. With electrical steel, I measure no obvious difference. If there is any difference, the non-annealed electrical steel is better than annealed one. The non-annealed electrical steel sample gives about 5% more measured voltage than annealed sample (but measurement error might be larger than that). In addition, annealed electrical steel does not seem any easier to bend. So, no benefit from annealing electrical steel (or I don't know how to do it properly). I did however see some improvements with bright-drawn mild steel. The sample B1 produces higher measured voltage than the sample B2. The difference is larger at smaller flux densities (I don't know why - I don't think my sample reached saturation in any case). What surprised me even more is that that the difference is larger at higher frequencies (I would expect otherwise - puzzling). Excitation current 90mA, 20Hz: Sample B1 -> 7.5V; Sample B2 -> 6V (cca 25% difference in measurement) Excitation current 90mA, 80Hz: Sample B1 -> 27.5V; Sample B2 -> 20.5V (cca 34% difference in measurement)) Excitation current 300mA, 20Hz: Sample B1 -> 25.5V; Sample B2 -> 23.5V (cca 9% difference in measurement)) Excitation current 300mA, 80Hz, Sample B1 -> 90V, Sample B2 -> 77V (cca 17% difference in measurement))
  2. But isn't processed food invented to decrease food waste?
  3. Mostly for fun, I would like to try annealing some small steel pieces (say, half inch size or less). Tips? What would be most easily obtainable tools to do it? What kind of torch should be enough - or should I build a wire heater? They say: soak it at correct (red-heat?) temperature for some time (seconds, minutes?) and then slowly (how slowly?) cool it down. I guess such small peaces would cool to quickly in air? Some internet guys also say that you should not heat it too much (orange). I don't understand how can this be a problem?
  4. This points out why I think that our Universe is unlikely a simulation - my argument is similar to why the Universe is unlikely a fluctuation. A rational programmer makes a minimal simulation, not a 'maximal' one.
  5. Beautiful (expressing the g-factor as a ratio of two frequencies where frequencies can be measured very accurately). It does however seem to me that the method assumes certain confidence in equations - that is, that Larmor and cyclotron frequency formulas are both very linear in respect to B. It seems that spin angular momentum of electron is usually obtained indirectly by measuring magnetic moment and assuming that formulas are right. Still, I did find one example where spin seems to be measured more directly - wikipedia calls it Einstein-de Haas effect: https://en.wikipedia.org/wiki/Einstein–de_Haas_effect
  6. But this again measures the magnetic moment, no? I don't know how to obtain the g-factor from this data - to obtain the g-factor, shouldn't I also have a direct measurement of the angular momentum?
  7. When I ask google how is the spin angular momentum of an electron measured, it points me to the Stern-Gerlach experiment. Yet, I figure, it cannot be the only way... As I understand it, the Stern-Gerlach experiment actually measures spin magnetic moment, but I guess there is some other way to measure the spin more directly - how else would we know the 'g' factor of an electron?
  8. Hmm, there are also irrational hopes. I was always worried how could science compete with those guys that promise eternal life. Another thing is spite (or whatever you would call this: "Fu** you and your fu**ing math! Yes, I don't understand it, so what?! I'm not a lesser person! So, fu** you and your damn physics!"? )
  9. This is the part that I don't understand... If they asked me, I would tell them exactly the same. You have two sensors, so compare them. Don't make electronics bossy, but assisting.... How come they didn't think of it? I am sure they did - I bet somebody intentionally decided otherwise, and this somebody did not act as an engineer when making the decision. (That said, I think regulatory bodies share the same responsibility in this case as the Boeing.)
  10. This is what I actually wonder - does a quantity obtained that way has any known meaning? For the momentum I obtain imaginary results which suggest it does not have a meaning. For kinetic energy I obtain real result. It might have a meaning. I used this to derive something that seems to me as the 'kinetic energy density' function. But I never heard of such thing before.
  11. Must every boson mean a force? (Higgs boson too?)
  12. Difficult one, but someone might know: At what moment in history are magnitudes of units of electric field (volts per meter) and of magnetic field (tesla) adjusted just right so that we don't need ugly constants in laws like Lorentz law or Faradays law of induction? Was this also the case in dark times before SI units?
  13. It might make sense... If the fluid velocity at about 10 meters per second (22mph) and if the magnetic field is 1 tesla (quite strong) then you can have 0.1V per each centimeter of the width of the fluid flow. So I guess if the flow and the magnetic field is wide enough (20-30 centimeters or more) and if other conditions are just right, you can have some electrochemical effect. I however am not very good at chemistry and maybe someone else wants to comment how much voltage is actually needed to start electrolysis (or whatever).
  14. If the system is stationary, then no. If the alloy sheet moves relative to magnets, then still probably no. (Any voltage difference that you might achieve with this simple settings seems unlikely to reach some electrolysis threshold - although my knowledge about electrolysis is low.)
  15. I heard some amateur astronomers complaining more about bluish light than about reddish light when making observations (I guess, blue disperses more causing more light pollution). I also heard somewhere, but I cannot remember how much was this reliable, that night animals might get disturbed more by bluish light than by reddish light. Anyone heard about this? For me, the ideal street lighting would adjust its intensity during the night - decreasing its power and shifting more red after 23:00h... I guess it might also adjust to foggy conditions somehow... or even to moonlight intensity.
  16. Hmm... but let's compute expectation value for kinetic energy... I am doing this for the same wave-function (ground state particle-in-a-box): ('h' is actually h-bar) The above is the correct result when the integral is computed over the whole box. But even if I integrate over only a part of the box, I still obtain real values - does it mean that such result might have some actual meaning? Not being lazy, I tried to compute kinetic energy distribution (or density) over the box. Moderators can move this to the speculation forum. I am using a sloppy notation as I know no better. This is the kinetic energy density function for a ground-state particle in a 1D box, how I calculated it.... Can this have any meaning? The function shape resembles the position probability density function for the particle. I would be very glad if there is any function that can show kinetic energy density for wave-like particles. I like energy distributed in space (that is, local i like the local conservation of it). However, I never heard anything about it.
  17. So, from various sources this is an time-independent wave-function for a ground state particle in an infinite square (widht 'a'). The momentum calculation gives zero, as expected. But if I only integrate over half of the box width (the last line) then I get an imaginary result. Does this mean that this result has no interpretation (that it, it means nothing)? [sorry, the 'h' should actually be h-bar, but I don't have this symbol]
  18. Hello... Say there is a particle in a 1D box. The particle is in certain state. I know its position-space wave function. I can compute expectation value of its momentum by sandwiching the momentum operator between psi* and psi and integrating over the whole box width (or over whole infinity). Question... If I don't integrate over the whole box, but only over a part of the box, can the result be interpreted as follows: if I simultaneously measure momentum and position of identically prepared setups, and if I only consider those cases where a particle was found within the part of the box for which I computed the integral, then the average momentum of those particles will equal to my integral?
  19. Yes, it makes sense to me too... In fact, I guess that the spin-flipping due to the thermal agitation is the reason why paramagnetic materials stop being paramagnetic when removed from an external field. In the meantime I tried to find more argon data to check if argon energy levels are spaced close enough to be excited by room-temperature collisions... unsuccessfully... But I guess not. Anyway, it is my 500th post, and I am giving +1 to everybody... you lucky devils!
  20. I understand... I abandoned the idea that rotation of atoms can be used as energy storage (to aid heat capacity). I can accept that atom rotation is not a thing. I am investigating now if electron energy transitions in some heavier atoms are small enough to count as 'unfrozen' degrees of freedom for heat storage.
  21. Ok, I see that the 'rotating atom' is a problematic idea. Some back of the envelope calculations, if I did it correctly: Average kinetic energy of a gas particle at 300K is about 0.04eV; The 1420MHz photon has about 6 micro-eV. Therefore, the thermal motion cannot excite an electron in a hydrogen atom from 1S to 2S, but it should be able to flip-flop its spin easily. Is this happening in a real gas? (I guess it might be happening in monatomic hydrogen, but not sure about H2 - probably spin cannot be flipped in H2?) Next, if we are dealing with heavier atoms (say argon) then I expect external electrons have smaller difference between energy levels - possibly comparable to 0.04eV. Should I then expect that those electrons in argon contribute to the heat capacity of argon gas? I guess you are referring to the very high (10.2eV) temperature needed - not that there is some other limitation why collisions are unable to excite quantum states?
  22. Hmm... I guess, one way to know that they are rotating is by measuring heat capacity of the gas (and from this we know that they are NOT rotating). But this is a proof of neither, imo. Because atoms are not solid bodies, I guess that their rotation would mean a net non-zero rotation of all the parts. So, when thinking about your last sentence, I guess that my question should actually be: why in monatomic gases, thermal excitation do not cause change in orbital momentum of atom's external electrons? Is this a better way to ask? (I really am not sure what I am talking about - I am just learning the new stuff here).
  23. in monatomic gases, why isn't atom rotation taken as one possible degree of freedom - that is, why energy cannot be stored in atom rotation? Is this degree of freedom non-existent or just frozen? Google finds many answers, but they seem to differ. Some say that rotation is simply not physical (whatever it means), some say that a single quantum of rotational energy is much larger than available energy at normal temperatures...
  24. I read about Oliver Heaviside - people mention his eccentricity. Among other things, he apparently liked heating his home to levels uncomfortable for most people. Sources don't tell if he preferred smoothies over coffee.
  25. I tried to sketch motor torque curves (at nominal and reduced voltage) and some hypothetical load torque curve (a constant-torque load - red line in the graph). You can see how, with reduced motor voltage, the motor will settle at lower speed (lower rpm). This means that its slip increases (the slip says how much its speed is reduced in comparison to the synchronous speed). The thing is that the current the motor draws (its impedance, if you want) very much depends on the slip. As a result, at the reduced voltage the motor will draw significantly more current (It might go above its nominal current causing overheating and stuff, despite the fact that the delivered torque is still at the motor nominal level). As you can understand, some load curves (like that of a fan) will not cause so much problems with a decreased voltage as some other load curves might (the displayed constant-load curve is a bad one).
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.