0 Members and 1 Guest are viewing this topic.
EMF for non-thin-wire circuitsIt is tempting to generalize Faraday's law to state: If ∂Σ is any arbitrary closed loop in space whatsoever, then the total time derivative of magnetic flux through Σ equals the EMF around ∂Σ. This statement, however, is not always true and the reason is not just from the obvious reason that EMF is undefined in empty space when no conductor is present. As noted in the previous section, Faraday's law is not guaranteed to work unless the velocity of the abstract curve ∂Σ matches the actual velocity of the material conducting the electricity.[28] The two examples illustrated below show that one often obtains incorrect results when the motion of ∂Σ is divorced from the motion of the material.Faraday's homopolar generator. The disc rotates with angular rate ω, sweeping the conducting radius circularly in the static magnetic field B (which direction is along the disk surface normal). The magnetic Lorentz force v × B drives a current along the conducting radius to the conducting rim, and from there the circuit completes through the lower brush and the axle supporting the disc. This device generates an EMF and a current, although the shape of the "circuit" is constant and thus the flux through the circuit does not change with time.A wire (solid red lines) connects to two touching metal plates (silver) to form a circuit. The whole system sits in a uniform magnetic field, normal to the page. If the abstract path ∂Σ follows the primary path of current flow (marked in red), then the magnetic flux through this path changes dramatically as the plates are rotated, yet the EMF is almost zero. After Feynman Lectures on Physics Vol. II page 17-3
I have tried to move a wire in front of a magnet, and I can see some current was generated in the wire by the reading of a milliammeter. The current must form a closed circuit to enable reading. A short conductor falling in a magnetic field may generate eddy current which in turn resist its movement, but it still requires a closed loop.In my experiment, I can only find one bump of current reading when a neodymium magnet is moved pass the milliampmeter's wire which forms a closed circuit. This agrees with Faraday's law that the current is proportional to dB/dt. With finite speed, there would be no vertical line on the oscilloscope.
A short conductor falling in a magnetic field may generate eddy current which in turn resist its movement, but it still requires a closed loop.
The Bored chemist has solved it, but he is ashamed to tell us the solution, because he loses as usual.
Quote from: Mitko Gorgiev on 28/02/2020 00:11:28The Bored chemist has solved it, but he is ashamed to tell us the solution, because he loses as usual.Until you stop messing about and actually answer the question I asked, I don't know what you are talking about.Consequently, I can't "solve" it.I'm obviously not ashamed of your inability to answer a question.I don't have anything to lose here; I'm still trying to find out what you are talking about.
What short conductor?
I don't believe in your experimental setups
Quote from: Mitko Gorgiev on 28/02/2020 11:33:31What short conductor? See this video. Skip to 2:50//www.youtube.com/watch?v=YVYZSsNDSVg
You link a video which doesn't have anything to do with the problem we discuss and you avoid to answer my questions.
Quote from: Mitko Gorgiev on 29/02/2020 15:00:40You link a video which doesn't have anything to do with the problem we discuss and you avoid to answer my questions.Well, I understood the relevance.Why don't you?
Would you answer the questions for Hamdani?
Quote from: Mitko Gorgiev on 29/02/2020 15:05:37Would you answer the questions for Hamdani?You seem to have forgotten who was asking questions.Quote from: Mitko Gorgiev on 28/02/2020 11:33:31What short conductor?
So, let me remind you: Question 1 (figure (a)):In which case the current will be stronger? When the conductor is moving from A to B or when it is moving from A1 to B1?Question 2 (figure (b)):What will happen when the conductor is moving from A to C through B? How will the induced current change?If you answer my questions, I will answer you why I think that the linked video has nothing to do with the subject here and also other unanswered things, if any.
It depends on the distribution of magnetic flux density in the space cut through by the wire, including the return path to the amperemeter. BC has pointed out that the field is not parallel near the end of the magnet.The video below shows how the magnetic field is distributed around a permanent magnet.//www.youtube.com/watch?v=74eGPu5L0iw
Some people do not want to admit the truth regardless of how strong are the proofs someone brings forward.
Quote from: hamdani yusuf on 02/03/2020 04:43:07It depends on the distribution of magnetic flux density in the space cut through by the wire, including the return path to the amperemeter. BC has pointed out that the field is not parallel near the end of the magnet.The video below shows how the magnetic field is distributed around a permanent magnet.//www.youtube.com/watch?v=74eGPu5L0iwThis is not an answer. This is only complicating a very simple question, which means avoiding to answer it. I have already answered one of the questions here:.https://www.thenakedscientists.com/forum/index.php?topic=78772.msg594433#msg594433I think that this is a problem of morality. Some people do not want to admit the truth regardless of how strong are the proofs someone brings forward. And it has to do with the moral.
Quote from: Mitko Gorgiev on 02/03/2020 20:03:36Quote from: hamdani yusuf on 02/03/2020 04:43:07It depends on the distribution of magnetic flux density in the space cut through by the wire, including the return path to the amperemeter. BC has pointed out that the field is not parallel near the end of the magnet.The video below shows how the magnetic field is distributed around a permanent magnet.//www.youtube.com/watch?v=74eGPu5L0iwThis is not an answer. This is only complicating a very simple question, which means avoiding to answer it. I have already answered one of the questions here:.https://www.thenakedscientists.com/forum/index.php?topic=78772.msg594433#msg594433I think that this is a problem of morality. Some people do not want to admit the truth regardless of how strong are the proofs someone brings forward. And it has to do with the moral. Unexpected results come from false assumptions. One of yours which I can identify is assuming that magnetic field lines around a magnetic pole are parallel, which is demonstrably false by the experiment. When the magnetic field lines are parallel, and we move the magnet relative to conductor along those lines, we got no electric current, as I have shown in my own experiment.If you have some idea regarding truth and morality, feel free to join my discussion in a thread about universal morality.
, analyze how much you will what is the field around an ORDINARY CYLINDRICAL MAGNET and then answer the questions.
I have uploaded an experiment video on electric generation by moving magnets through a coil.//www.youtube.com/watch?v=MyrpcjIJ3kwLet us know if the result agrees with your expectation.