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# Physics/What about the brush noise (pulse signal) of a DC motor

Question
QUESTION: Dear Sir,

I have a ferrite coil and would like to send a pulse signal through it, the science magazine suggests a DC motor which works between 6-12 volts. It is said that the brush noise from the DC motor is providing a pulse signal to the coil.
Hmmm, what kind of pulse would this be, I am curious, if I use a simple toy motor with an electrical potential of, lets say 9 volts ?
It this a kind of full wave rectification wave, with a disturbed (not harmonically) wave character ?
Hmmm, what would happen, when I use a signal generator with different frequencies and send the current to the coil, after a full wave rectification through a diode bridge ?
Here I can play with the DC frequency, am I right ? The pulses that I send would not be disturbed anymore, which other positive effects can you mention ?
Is here a limitation on the sent frequencies, for example can I send rectified AC currents in kHZ or MHz values, why ?

In which situations is it better to use a motor described above, to pulse the DC current input and in which situations should we rectify the current output of a signal generator over a diode bridge ? Why ?

Are both effects the same ?

Birol

ANSWER: It said noise, and I would assume that's accurate, given that it's brush noise from electrical contact.  So not any kind of characterizable wave, but noise.  Also, why would you want to send a signal through a ferrite coil?  A choke like that is intended to squelch noise and pulses.  And what do you mean by DC frequency?  DC means direct current, so there's no frequency involved.  The rest of your question makes absolutely no sense, perhaps you can rephrase it.  Again, you don't "pulse a DC current."  That's a contradiction in terms.

---------- FOLLOW-UP ----------

QUESTION: Hello Steve,

Thank you for your try. Hmmm, I want to send the current from a battery to a coil like structure,the motor here should pulse the coil, I mean DC pulses (pulsed DC), like rectified AC, do you understand ?
What happens to the wave of the current if you send it through a motor (with brushes) this is the main point of the question, a current with noise, can you sketch me the graph ?

Birol

I understand perfectly well.  DC is direct current.  AC is constantly time-varying current in a sinusoidal waveform.  I teach this and have for many years.  You're talking about transients, which are not DC signals.  They're pulses.

Noise cannot be sketched as a graph, it's random by definition.  You can sketch your own graph of random noise, I suppose, it's just noise.

Physics

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#### Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.