# Discharging a capacitor faster using an external B-field?

• PhiowPhi
In summary: However this would defeat the purpose of using a variable capacitor in the first place.In summary, it is possible to increase or decrease the discharge rate of a capacitor by aligning the time-varying external magnetic field with the magnetic field produced by the displacement currents.
PhiowPhi
If a capacitor is being discharged and the electric field is varying with time producing the displacement currents, wouldn't it be possible to align a time-varying external magnetic field with the magnetic field produced by the displacement currents to increase the discharge rate? Or the vice-versa slow down the discharge rate?

$$B_{Net} = \Delta B_d + \Delta B_{ext} ∴ \uparrow t_d$$
$$B_{Net} = \Delta B_d - \Delta B_{ext} ∴ \downarrow t_d$$

Where,
##t_d##: The discharge time.
##B_{Net}## : The net magnetic field within the separation region.

From Ampere's law it seems plausible:

$$\oint_C {Bd\ell = \mu _0 I_C }$$

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Nik_2213
The time varying magnetic field can encompass the space between the capacitor plates or the connecting wires with equal effect. It will induce a voltage in series with the circuit by electromagnetic induction, and is equivalent to placing a dynamo in series with the circuit. If the polarity is such as to aid the flow of current, the capacitor will discharge quicker.
The energy supplied by the dynamo will be expended in additional heating of R.

anorlunda
#PP: Slightly tangential but, given many capacitors are 'rolled up' for volumetric efficiency, and air-gapped variable capacitors are usually multi-plate, so the effects of an external magnetic field would cancel, you'll have difficulties applying this tweak.
Kudos for the lateral thinking !

sophiecentaur
Is this a thought experiment or is there a practical aspect to it. Is the aim to discharge the capacitor as fast as possible or is it to pass a high current through the R?
I'm sort of looking for a Switch somewhere in the circuit??
The current through the load R will depend on the voltage across it.

The need to discharge a capacitor rapidly is usually encountered when resetting a charge integrator circuit. Unfortunately the current in the inductance of the coil needed to generate the magnetic field takes longer to build than does short circuiting the capacitor, and then you must wonder what will happen when you try to turn off the magnetic field.

To discharge 1 volt, from a 1 farad capacitor, in 1 second, would only need a current of one amp. To discharge it in 1 nanosecond would require an impossible Giga-amp. By employing commutation, a charge integrator of any capacitance, can be used to generate a sawtooth waveform with a one nanosecond transition time.

Why do you need to discharge the capacitor so quickly?

I can't help thinking that the OP could be putting the cart before the horse. Any question of this nature just has to have the How Fast, What charge, what Capacitance ? information if a serious answer is expected.
One obvious solution would (could, depending on the actual requirement) be to switch in a massive capacitor in parallel to take most of the charge and then discharge the sink capacitor at your leisure.

## 1. How does a B-field affect the discharge rate of a capacitor?

A B-field, or magnetic field, can induce a current in a nearby conductor, including the conductive plates of a capacitor. This induced current can help discharge the capacitor faster by providing an alternate path for the flow of electrons.

## 2. Can any type of B-field be used to discharge a capacitor faster?

No, the B-field must be changing in strength or direction to induce a current in the capacitor. A steady magnetic field will not have the same effect.

## 3. What is the advantage of using an external B-field to discharge a capacitor?

The advantage is that the external B-field can accelerate the discharge process, allowing for a faster and more controlled release of stored energy. This can be useful in applications where a quick discharge is necessary, such as in flash photography or in electronic circuits.

## 4. Are there any potential risks or drawbacks to using an external B-field to discharge a capacitor?

If the B-field is too strong, it could potentially damage the capacitor or other electronic components. It is important to carefully control and monitor the B-field strength to avoid any potential risks.

## 5. Can a capacitor be discharged faster using multiple B-fields?

Yes, using multiple B-fields can further accelerate the discharge process. This is because each B-field can induce a separate current in the capacitor, leading to a more rapid release of stored energy. However, the B-fields must be carefully coordinated to avoid any interference or potential damage to the capacitor.

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