Recent content by cabrera

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    Mathematica Automatically create array of named variables

    ListPlot will iterate over a list of expressions: P = Table[Indexed[p, i], {i, 1, 7}] pointList = Table[{RandomReal[{0, 3}], RandomReal[{0, 3}]}, {i, 1, 7}] Manipulate[ ListPlot[P, PlotRange -> {{0, 3}, {0, 3}}, Joined -> True], {{P, pointList}, Locator}]
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    Nyquist theorem & collecting digital values

    You need to add a anti-aliasing filter with a roll-off at half of the sampling frequency of the ADC
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    How to calculate the counter-electromotive force of a motor?

    Thanks for your help
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    How to calculate the counter-electromotive force of a motor?

    Dear Forum, I would like to get familiar with motors. I "think" I understand the basic principles of DC motor: 1) Fix magnetic field (stator), Bf 2) Rotating magnetic field( rotor), Br 3) Force (Torque) proportional to intensities of Bf, Br, angle 4) Commutation of loops to keep Br at constant...
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    IF amps for a superhet AM receiver

    Hi, first of all I have been following this topic as I always wanted to built a transceiver. I don't know much about this type of transformer but I guess that you have to check the impedance ratio between the primary and secondary windings. The data sheet only shows a single impedance ratio...
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    PNP versus NPN bipolar transistors

    Hi, Could anybody explain me why the base current of a pnp is higher than a npn for the same collector current? Regards, David
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    Graduate Stuekelberg interpretetion of anti-particles

    Dear Forum, I have discovered by accident the method developed by Feynman and Stuekelberg to explain the origin of antiparticles ( I have the little book "Elementary particles and the laws of physics). As you might be all aware by using basic perturbation theory and assuming that negative...
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    Undergrad What is the complete expansion of |1+a|^2 for a complex number a?

    Hi, Could you help me to understand the following expansion I found in a book of qunatum mechanics. |1+a|^2=1+a+a*+... where a* is the complex conjugate of a
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    Graduate Magnetic field relativistic effect

    WannabeNewton, what is a Lorentz boost?
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    Graduate Magnetic field relativistic effect

    Sudu, But the force that the charge "feels" is from a electric field. It is us who decide where the frame is. But as far as the charge is concerned there is only an electric field. Same problem can be solved with different physics depending of where the framework is, which I found no less...
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    Graduate Magnetic field relativistic effect

    Vanadium 50, I assumed it was a relativistic effect(the magnetic field) from the electric field. As I said, the force on a charge moving at speed v induced by a current density, J, in a wire could be explained either by a magnetic field, if the frame is at rest, or an electric field if the...
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    Graduate Magnetic field relativistic effect

    Hi Forum, It is said that the Magnetic field is a relativistic effect. I went to the Feynman lectures on Physics and found an example based on the force a charged has when moving at speed v next to a conductor with a current density J. I understand that the framework at rest uses a magnetic...
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    Finding electric potential with non-uniform charge density?

    physwizard, I meant inside the shell. The field should zero,shouldn't it?
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    Finding electric potential with non-uniform charge density?

    The electric filed is zero. Gauss theorem. The volume inside does not have a charge. You cannot have a closed surface with a charge inside, ∇ρ=0, because all the charges are distributed on the surface. That's the reason why the electric field inside a metal is zero. But the potential is cte or...
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    Finding electric potential with non-uniform charge density?

    Have tried ∫sin² x dx = ½ x − ¼ sin 2x + C?