Jump to content

Danijel Gorupec

Senior Members
  • Content Count

    594
  • Joined

  • Last visited

  • Days Won

    2

Danijel Gorupec last won the day on July 19

Danijel Gorupec had the most liked content!

Community Reputation

90 Excellent

About Danijel Gorupec

  • Rank
    Molecule

Contact Methods

  • Website URL
    http://charming.awardspace.com

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. If it is a scam, that might tell us more about European Union than about nuclear fusion. From this single failure (of ITER) my first thought is that governments are incompetent, and only then that fusion might be a scam.... It will take several failures coming from different parties to convince me that fusion does not pay.
  2. Very nice, Moontanman... as you once proposed and I accepted as more logical.
  3. Thinking out loud... At the time, Einstein did not have to feel embarrassed because he didn't know how to reconcile his theory with QM. If one would be developing GR some 40 years later, he would be under some pressure to provide a theory that includes QM. Some guys/girls might abandon their work out of frustration... So maybe, we won't ever have GR as it is now, but we would directly have (eventually) a version given with QM in mind.
  4. @studiot Thanks. I obtained the book (obviously a different edition than yours). Looks fine, will try to read some interesting chapters in my spare time. I am considering electric and magnetic fields because I know them better. The gravitational field might be simpler from the potential energy point of view, but I wouldn't know how to handle its filed energy. Furthermore, the ultimate problem I am considering (what does it mean when we say that electron shifts its energy in magnetic field, like in the Zeeman effect) is related to electric and magnetic fields. @swansont Great that you introduced the capacitor example - it is simple enough that I can make some calculations (see below). But first to answer your 'philosophical' question... Yes, these are two ways of doing calculations. But, imo, not equivalent... The 'field energy' is more precise. Specifically, it precisely defines how the energy is distributed in space (energy density distribution). The 'potential energy' obscures this information. The energy distribution is important for the local energy conservation idea. Imo, if you cannot tell the energy distribution, then the idea of local energy conservation becomes moot. As I take the local energy conservation as a strong requirement, so I think that, at least in principle, we should be able to describe each form of energy by its energy density distribution... It is for this reason that I expect that each forms of potential energy is describable by field energy (or at least by some other way that does not obscure the energy distribution information). As you know from my other thread, I found one example (spin magnetic moment in external magnetic field) where I cannot relate the potential energy change to the field energy change and this itches me. Now the computations... they are striking... We consider a charged plate capacitor. During the experiment, the plates are moved from the starting distance d1 to the ending distance d2. We compute the potential energy change (first line of equations) and field energy change (second line of equations). CASE 1 - constant charge. Everything is clear here and everything fits nicely. The PE change equals the field energy change. CASE 2 - constant voltage. This is interesting. When we look at the system from the potential energy viewpoint, the total energy of the world does not fit! But when we look from the field energy viewpoint, everything fits nicely. Note that in the total energy of the world must include the energy in the idealistic battery that is used to ensure the constant voltage on the capacitor. Note that in the constant-V case the field energy decreases as we are separating the plates. However the energy that is 'pumped' back into the battery is twice the work done... The potential energy viewpoint would give balanced energy only if you avoid looking into the energy change of the battery. Once you peek inside your battery, your energy balance falls apart. So, if I didn't do any major mistake in my reasoning, it seems that the field energy is more precise and more fundamental than the potential energy. If one really, really wants to give a precise answer to the question 'and where is the energy stored' he/she should give the answer from the field energy viewpoint and should avoid the potential energy viewpoint. What do you think?
  5. I am investigating the relation between potential energy and field energy. I think electric and magnetic fields might be simplest to consider. Imagine a simple system of two small charged particles (not elementary particles) separated some distance apart. - we define that the potential energy of this system is U0. - we compute that the energy stored in the electric field is: E0 (note: we computed E0 by integrating the energy density formula for the electric field over the whole space. No need to consider our particles as point charges - say they contain uniformly distributed finite amount of charge in a small finite volume.) We slowly separate the two charged particles some distance farther apart. To do this, we invested some work W. What is now the potential energy U1 of the system? Is it: U1=U0+W? What is now the field energy E1? Does it equal to E1=E0+W? What is the change of the total energy of the system - does it equal to W? My opinion: Yes, the U1=U0+W; yes, the E1=E0+W; and yes, the total energy change equals W. Therefore the change in potential energy and the change in field energy represent the same thing. We should consider either potential energy or the field energy when we compute energy balance. We cannot consider both energy changes as we would be doing double-counting error (in our example, we might compute that the energy difference is 2W instead of W). Let's be stubborn and try the opposite anyway.... let's suppose that potential energy and field energy are two separate things. In this case we could claim: U1=U0+x*W E1=E0+(1-x)*W (where x is a number between 0 and 1) Using these claims the energy will still balance (the energy change is x*W+(1-x)*W=W), but the question would be what is the factor x? Is it x=0.5? Why? So, can we safely say that the change in the potential energy and the change in field energy represent one the same thing? Are there exceptions?
  6. Hmm... What do I do now - I don't find this answer that much revealing because I feel that terms 'interaction energy' or 'potential energy' are intentionally obscuring (they seem like aggregate terms used when it would be too complex to look into full details). Should I open another thread to clarify the difference between potential/interaction energy and field energy?
  7. I think, if our civilization continues without a reset, we will very soon start to intentionally change ourselves at a rate much faster than natural evolution could do. We will engineer our genetic codes (we will also install non-living implants into our bodies to obtain above-natural capabilities and we will even create self-reproducing machines not based on DNA that will continue to evolve themselves at an 'explosive' rate).... So, ironically, the 'intelligent design' might soon be thought as a mainstream
  8. I believe you introduced the concept of potential energy. Specifically, the potential energy of magnetic dipole in magnetic field. But isn't the idea of potential energy just a shorthand that we use? Isn't it always more precise to deal with the energy stored in the field? That is, I assume that the potential energy change (due to electromagnetic field) can always be represented as the electromagnetic field energy change. The trouble is that I continuously fail to relate the potential energy of our elementary-charged-particle-with-spin to the field energy! If the particle really changes its potential energy, and this is not mirrored in the field energy, should I then accept the the potential energy is something really fundamental (not just a shorthand)? I just cannot imagine the potential energy as a thing on its own. Oh, and yes... you might think that the energy shift of the particle is stored is in the magnetic field, but I don't think so (the energy stored in magnetic field seems to shift in a wrong way - it decreases when the electron shifts its energy up.)
  9. Thanks guys... I am glad that studiot used the term 'energy repository' as I think what bothers me is understanding how the energy is stored during these energy shifts. So could the 'spin' be a possible way to store energy? It would surprise me as the quantum spin is fixed (it can measure only two discrete values of identical magnitude). Here is what I think is the essence of my troubles: A simple atom, with only single electron in a state that only has spin magnetic moment (zero orbital magnetic moment) is immersed into magnetic field. Electron's energy shifts... But there is nothing measurable that changes about this atom. I expect that its orbital shape remains unchanged, and its spin (if measured) remains unchanged. Except, of course, its mass does change (from Einstein) - but is this it, is this mass change all that I should expect to happen with this atom?
  10. I would like to understand better how atomic orbitals behave in (magnetic) fields... After reading about Zeeman effect, I understand that electrons bound in an atom might shift their energies when placed in magnetic field. I ask if this energy shift is also associated with some change in the shape of their orbitals? (I guess, this is equivalent to asking if the probability density function changes). I would expect that orbitals that have some angular momentum (and magnetic moment) do change their shape. I read that atoms near a magnetar star could look needle-shaped... But I don't see how would an orbital with zero angular momentum (and zero magnetic moment) change its shape? On the other hand, if no change in orbital shape (probability density) can be associated with electron energy shift in magnetic field, how do then electrons 'shift' their energies (do they speed-up, become heavier or what)?
  11. If you will be using your motors and generators near their intended regime (rotational speed, voltage, load), then it is often good enough to just look at the motor/generator nameplate - the efficiency should be stated there. It very much depends on the motor type, class, size... A small asynchronous motor (around 1kW) might be 80-90% efficient. Larger motors have higher efficiency than smaller ones. Technology makes difference too - a permanent magnet brushless DC motor are usually more efficient that equal-power common squirrel-cage asynchronous motor. High-efficency motors can cost significant money. However, if you will be using your motor in wide range of working regimes, just looking at the nameplate efficiency might not be good enough. For more expensive motors you will probably be able to obtain efficiency diagrams from the motor manufacturer. This would be perfect, because calculating it from first principles is difficult - you would need to know everything about motor construction to calculate it properly (in this case, it would be much easier to just measure it than to try the calculation). For qualitative analysis and orientation, you will be able to find various efficiency curves by googling. Some general efficiency notes: - the core loses are usually divided into two parts: hysteresis loses (depends on quality of silicon steel used in your motor - hysteresis loses are roughly proportional to the frequency, keeping other things the same) and eddy-current loses (depends on the resistance of silicon steel and lamination thickness used in your motor - these are roughly proportional to the square of the frequency). In a typical motor, at its nominal speed, the hysteresis and eddy-current loses are about the same. - the copper loses might be about the same as the core loses (in nominal regime). In some types of motor, these can be relatively easy to compute if you know motor current and winding resistance. - mechanical loses are usually divided into bearing loses and (in some constructions) cooling fan loses. Normally are smaller than copper loses and core (iron) loses. - motor efficiency very much depends on the load - the best efficiency is often when your motor gives 70-80% of its nominal load. At low loads, of course, the efficiency drops drastically. - you usually regulate your motor using some circuitry (motor driver). Modern semiconductor drivers (like inverters) can have efficiencies well above 90%. Still, take it in account. Only if you will be designing motors themselves, you will need to dig deeper than simply analyzing motor efficiency curves. Today you would be typically using computers and numerical-analysis software to compute your motor efficiency. Batteries are chemistry and not my area, but of course they have limited efficiency (as anything else). I see that a typical lithium-ion battery might have charge/discharge efficiency of about 80-90%. Of course, if you are not actually charging/discharging your battery, like in the case when you are generating just as much power as you are spending, then this efficiency is not a concern. But you will occasionally charge/discharge your battery (otherwise, you would not even have the battery in the first place). Another source of battery loses is the self-discharge. This means, a battery will lose some percentage of stored energy with time - even if you don't charge/discharge it. I understand that lithium-ion batteries have fairly small self-discharge, so unless you need a long-time storage it is not so much a concern. As everything else, I expect that battery efficiency depend on quality of construction, and this affects the battery price. Gearboxes can be made to have very high efficiency, fairly over 90% - but it again depends on the construction (worm gear is not very efficient, while helical gears can be). Unfortunately, a good gearbox can be surprisingly expensive as it requires high precision. A trivial example: you have an inverter (efficiency 95%) that runs a motor (efficiency 90%) that drives a gearbox (efficiency 95%) that drives a generator (efficiency 90%) that charges a battery over a rectifier (efficiency 97%). Later you discharge the battery (efficiency 85%) to produce electricity for something useful... The fact is that the electrical energy that you obtained from this battery is only about 60% of what you spent in the first place: total_efficiency=0.95*0.90*0.95*0.90*0.98*0.85. I cannot recommend any good source on the Internet - I am sure there must be many, but I just tend google for anything specific and usually find something useful. Hopefully somebody else will provide a good link.
  12. As Bufofrog said, you have no chance with the proposed motor-generator-battery setup. A certain amount of energy will be 'lost' in every step: - your motor has efficiency less than 100% and will 'lose' some energy as it converts electrical energy into mechanical energy - your generator has efficiency less than 100% and will 'lose' some energy as it converts mechanical energy back into electrical energy - your battery has charge/discharge cycle efficiency less than 100% and will give you less energy back than you previously stored into it. Increasing the rotational speed of the generator does not make any essential difference (although the gearing might give you the ability to keep the rotational speed of your motor and your generator at their best-efficiency range, but you will still lose energy. In fact, the gears will introduce additional energy loses, so it might not even decrease the overall loses). BTW, I did it when I was a kid - it did not work
  13. Yep, it does not make sense to split a thread and retain the same title.
  14. What is this thread about? Is it about climate change (as the title suggests) or about plant ability to make sugars (as I understand the first post)?
×
×
  • 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.