Question about Capacitor current and electromagnetic induction

[Esquilo]

Good morning, I can't understand a concept of electromagnetic induction. Then according to Biot Savart's law, at high and alternating currents (amperes) electromagnetic induction occurs in nearby conductors, if instead we have a capacitor (which accumulates a lot of voltage and a few amperes) which discharges into an inductor (RLC circuit) alternating currents and increases inductance, why does electromagnetic induction in nearby conductors not occur in this circuit? Because of the high voltages and low currents (ampere/second) of the capacitor?

 

[jbriggs444]

if instead we have a capacitor (which accumulates a lot of voltage and a few amperes) which discharges into an inductor (RLC circuit) alternating currents and increases inductance

I do not understand your characterization of this capacitor. A capacitor accumulates charge and, as a consequence, attains a high potential difference between its terminals. It does not accumulate amperes.

Perhaps you mean to say that a capacitor can attain a large potential difference from a small amperage given sufficient time.

If you discharge such a capacitor through an inductor without a resistor (just a capacitor and an inductor back to back in an LC circuit) that will product an alternating current, yes. This does nothing to change the inductance of the inductor.

If you discharge the capacitor through an inductor in series with a resistor, that is an RLC circuit which may or may not result in an alternating current depending on whether it is overdamped, underdamped or critically damped.

Normally when we look at a circuit diagram, we are adopting a "lumped element" model where no component has any effect on any other component except through the wires in the diagram. The elements only have their nominal behavior. No electromagnetic radiation from any wire or element has any consequence elsewhere in the circuit.

 

[Herman Trivilino]

why does electromagnetic induction in nearby conductors not occur in this circuit?

Do you understand how transformers work?

 

[Esquilo]

I do not understand your characterization of this capacitor. A capacitor accumulates charge and, as a consequence, attains a high potential difference between its terminals. It does not accumulate amperes.

Perhaps you mean to say that a capacitor can attain a large potential difference from a small amperage given sufficient time.

If you discharge such a capacitor through an inductor without a resistor (just a capacitor and an inductor back to back in an LC circuit) that will product an alternating current, yes. This does nothing to change the inductance of the inductor.

If you discharge the capacitor through an inductor in series with a resistor, that is an RLC circuit which may or may not result in an alternating current depending on whether it is overdamped, underdamped or critically damped.

Normally when we look at a circuit diagram, we are adopting a "lumped element" model where no component has any effect on any other component except through the wires in the diagram. The elements only have their nominal behavior. No electromagnetic radiation from any wire or element has any consequence elsewhere in the circuit.

thanks for your answer, I am taking into consideration an RLC circuit in parallel, what I don't understand is, in the capacitor which accumulates electric charge, after discharge in the inductor which accumulates in the form of magnetic energy, here, this inductor which has accumulated inductance according to the formula L=VS/A can it induce electromagnetic induction in another conductor, even if it has a few milliamps since the capacitor does not accumulate any? my confusion comes from the biot-savart law which says that to have a good magnetic field you need to have a lot of current

 

[Esquilo]

Do you understand how transformers work?

thanks for your answer, I am taking into consideration an RLC circuit in parallel, what I don't understand is, in the capacitor which accumulates electric charge, after discharge in the inductor which accumulates in the form of magnetic energy, here, this inductor which has accumulated inductance according to the formula L=VS/A can it induce electromagnetic induction in another conductor, even if it has a few milliamps since the capacitor does not accumulate any? my confusion comes from the biot-savart law which says that to have a good magnetic field you need to have a lot of current

 

[jbriggs444]

thanks for your answer, I am taking into consideration an RLC circuit in parallel, what I don't understand is, in the capacitor which accumulates electric charge, after discharge in the inductor which accumulates in the form of magnetic energy, here, this inductor which has accumulated inductance according to the formula L=VS/A

"inductance" is not something that is accumulated. An inductor has a fixed inductance, no matter what you do to it.

I am not familiar with the formula: $L = \frac{VS}{A}$.
I would write it as $L = \frac{V}{dI/dt}$: the ratio of voltage across the inductor to rate of current change through the inductor.

Possibly there is a language issue here.

 

[berkeman]

An inductor has a fixed inductance, no matter what you do to it.

(except for when the current through the inductor approaches $I_{sat}$ in which case the inductance starts dropping...

 

[Esquilo]

"inductance" is not something that is accumulated. An inductor has a fixed inductance, no matter what you do to it.

I am not familiar with the formula: $L = \frac{VS}{A}$.
I would write it as $L = \frac{V}{dI/dt}$: the ratio of voltage across the inductor to rate of current change through the inductor.

Possibly there is a language issue here.

yes, sorry, I don't speak English and I'm just helping with the translator, yes the inductance depends on the physical characteristics of the coil, that's what I meant, and describes the ability of an inductor to oppose variations in current. but I still can't get my answers and that is, for there to be electromagnetic induction, there must be a high magnetic field density (B), but for there to be a high magnetic field there must be a lot of coherent flow (ampere) according to the law by biot-savart, but if a capacitor only accumulates charge (Q) and discharges it in the inductor, how can the inductor generate electromagnetic induction if the current (ampere) is very low?

 

[Esquilo]

(except for when the current through the inductor approaches $I_{sat}$ in which case the inductance starts dropping...

Hi berkerman i have the same question for you too I don't speak English and I'm just helping with the translator, yes the inductance depends on the physical characteristics of the coil, that's what I meant, and describes the ability of an inductor to oppose variations in current. but I still can't get my answers and that is, for there to be electromagnetic induction, there must be a high magnetic field density (B), but for there to be a high magnetic field there must be a lot of coherent flow (ampere) according to the law by biot-savart, but if a capacitor only accumulates charge (Q) and discharges it in the inductor, how can the inductor generate electromagnetic induction if the current (ampere) is very low?

 

[Herman Trivilino]

how can the inductor generate electromagnetic induction if the current (ampere) is very low?

The inductor generates a magnetic field whenever current of any magnitude flows through it. It's true that the magnetic field is relatively weak for a long straight piece of wire, but typically an inductor consists of many coils of wire often with an iron core. These features increase the strength of the magnetic field.

 

[berkeman]

Hi berkerman i have the same question for you too I don't speak English and I'm just helping with the translator, yes the inductance depends on the physical characteristics of the coil, that's what I meant, and describes the ability of an inductor to oppose variations in current. but I still can't get my answers and that is, for there to be electromagnetic induction, there must be a high magnetic field density (B), but for there to be a high magnetic field there must be a lot of coherent flow (ampere) according to the law by biot-savart, but if a capacitor only accumulates charge (Q) and discharges it in the inductor, how can the inductor generate electromagnetic induction if the current (ampere) is very low?

I'm with the other folks who have replied in this thread -- I'm confused with your use of technical terms in ways that don't really make sense to me.

Electromagnetic Induction is different from the Biot-Savart Law:

https://en.wikipedia.org/wiki/Electromagnetic_induction

https://en.wikipedia.org/wiki/Biot–Savart_law

The induced EMF (voltage) in a coil is proportional to the derivative of the magnetic flux $\frac{d\phi(t)}{dt}$ through that coil. So a larger flux and a more rapidly changing flux will induce a larger pickup voltage in a coil. The flux $\phi(t)$ is generated by currents, and is proportional to the number of Amp*Turns of the generating coil or conducting structure. To get the highest generated $\phi$ you use lots of turns in the coil and a larger current.

So given all of that, where are you introducing a capacitor in the circuit? Can you upload a sketch of the circuit that you are wanting to ask about? Use the "Attach files" link below the Edit window to upload your sketch or circuit diagram.

 

[jbriggs444]

yes, sorry, I don't speak English and I'm just helping with the translator, yes the inductance depends on the physical characteristics of the coil, that's what I meant, and describes the ability of an inductor to oppose variations in current.

Yes. I agree with this. The characteristics of the inductor affect its inductance.

for there to be electromagnetic induction, there must be a high magnetic field density (B)

This is not correct. One can have some induction with any flux density, no matter how small. Further, it is not the field that produces an electromotive force. It is changes in the field. Nor is it density that matters. It is flux density integrated over a surface. That is Faraday's law of induction.

[I did not know about Faraday's law until I looked it up in Wikipedia a few minutes ago]

but for there to be a high magnetic field there must be a lot of coherent flow (ampere) according to the law by biot-savart

Yes. Either a large current or a large number of turns of wire in a coil so that the same current circles the perimeter of the coil many times.

but if a capacitor only accumulates charge (Q) and discharges it in the inductor, how can the inductor generate electromagnetic induction if the current (ampere) is very low?

An inductor does not generate electromagnetic induction. It will have a potential difference if subject to a changing current. It is not the amount of current that matters. It is the rate of change of that current that matters.

In the absence of an inductor, an ideal capacitor short-circuited through an ideal wire will change from zero current to infinite current in zero time. That is a very high rate of change of current.

If you connect the capacitor to an inductor with a low inductance, it will take a large rate of change of current to result in a potential difference so that the voltage drop across the inductor matches the voltage currently on the capacitor.

If you connect the capacitor to an inductor with a high inductance, it will take a low rate of change of current to result in a potential difference so that the voltage drop across the inductor matches the voltage currently on the capacitor.

I do not really understand your concern. This is likely due to the language problem.

 

[Esquilo]

I'm with the other folks who have replied in this thread -- I'm confused with your use of technical terms in ways that don't really make sense to me.

Electromagnetic Induction is different from the Biot-Savart Law:

https://en.wikipedia.org/wiki/Electromagnetic_induction

https://en.wikipedia.org/wiki/Biot–Savart_law

The induced EMF (voltage) in a coil is proportional to the derivative of the magnetic flux $\frac{d\phi(t)}{dt}$ through that coil. So a larger flux and a more rapidly changing flux will induce a larger pickup voltage in a coil. The flux $\phi(t)$ is generated by currents, and is proportional to the number of Amp*Turns of the generating coil or conducting structure. To get the highest generated $\phi$ you use lots of turns in the coil and a larger current.

So given all of that, where are you introducing a capacitor in the circuit? Can you upload a sketch of the circuit that you are wanting to ask about? Use the "Attach files" link below the Edit window to upload your sketch or circuit diagram.

hi berkemann thanks for your answer, I'm not creating a project, it's all theory, the circuit under consideration is an RLC, in which the capacitor charges an inductor. but as you confirmed to me, you need a lot of current (amps) for there to be a high magnetic field density. therefore I believe that it is the variation over time, i.e. the discharge/charge of the capacitor that creates the electromotive force and therefore inverts the electrical energy accumulated in the capacitor into magnetic energy in the inductor, therefore I should have a high charge (Q) on the capacitor , Right?

 

[Esquilo]

Yes. I agree with this. The characteristics of the inductor affect its inductance.

yes thanks for the answer, ok I understand, so in an RLC circuit, in order for the inductor loaded by the capacitor to generate an electromagnetic induction which generates a variable voltage in the nearby conductors, the capacitor must have a lot of charge (Q) therefore a lot of voltage and capacitance (C), therefore it is not enough to have only the high capacitor voltage, but also the capacitance (C) which in practical terms corresponds to the ampere per second, but the mathematical calculations to calculate the inductance and the magnetic flux density (tesla) of the inductor in an RLC circuit where can I find them?

 

[Esquilo]

The inductor generates a magnetic field whenever current of any magnitude flows through it. It's true that the magnetic field is relatively weak for a long straight piece of wire, but typically an inductor consists of many coils of wire often with an iron core. These features increase the strength of the magnetic field.

Hi Mr. T, my problem came from the fact that according to the theory a capacitor accumulates only electrostatic (electrical) energy and in an rlc circuit, it discharges in an inductor, but if the inductor must transfer energy according to electromagnetic induction, how can the voltage of the capacitor alone, be able to generate a high magnetic field in the inductor?

 

[jbriggs444]

ok I understand, so in an RLC circuit, in order for the inductor loaded by the capacitor to generate an electromagnetic induction which generates a variable voltage in the nearby conductors, the capacitor must have a lot of charge (Q)

This is incorrect. Any amount of charge will do.

therefore a lot of voltage and capacitance (C),

If you want a lot of charge, you do not need a lot of voltage. Nor do you need a lot of capacitance. You need their product to be large.

therefore it is not enough to have only the high capacitor voltage, but also the capacitance (C)

As just mentioned, this is incorrect.

which in practical terms corresponds to the ampere per second,

Charge does not have units of ampere per second. It has units of amperes times seconds.

but the mathematical calculations to calculate the inductance and the magnetic flux density (tesla) of the inductor in an RLC circuit where can I find them?

Google is a start. I searched for "inductance from number of turns" and got an immediate hit.

I also tried "magnetic flux density of a coil" and got a formula for that.

 

[Herman Trivilino]

There's a huge language barrier in this thread. That's the problem.