Questions tagged [capacitance]

The ability of an object to store electric charge.

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Is the permittivity of a dielectric medium measured by application of radio frequency of 1 KHz and a resonant circuit of 1KHz are same?

I am working on a procedure in which I assess the dielectric constant of a medium by subjecting the dielectric medium to electromagnetic radiation of certain frequency (or the medium is subjected to a ...
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57 views

Capacitors in Series, which uses the most voltage?

AP Physics teacher here, preparing to teach my students about capacitors. We have some basic breadboards, capacitors, battery packs, and DC power supplies. My plan was to have them put three different ...
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48 views

Understanding the relation between the quantity of electric charge and capacitance

I was doing this excercise and, while I did it, I feel that I didn't truly understand how I got the solution. The excercice had a simple serial circuit of two capacitors, $C_1, C_2=4C_1$, resistor $...
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2answers
75 views

Why do generators need a complete circuit to move electrons but capacitors do not?

A charged capacitor will shock you if you come too close to it or touch it, and you are connected to the ground. A generator will only generate electricity if it has a complete circuit, it cannot just ...
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1answer
346 views

Earthing a system of parallel plates

our sir has taught us that when in a system of conducting infinite plates kept parallel to each other, when any one of them is earthed, then the charges present on the free ends(i.e. the open sides of ...
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201 views

Capacitance of octant of a sphere

What's the capacitance of octant of a sphere if the capacitance of sphere is C? I think that some combination of octants should make the capacitance of the whole. But what combination will it be ...
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1answer
54 views

Can electric field be restricted?

In high school physics, the electric field between a pair of NOT INFINTE paralle plate electrodes exists only between the plates, but now we know there are electric field lines curved out from the ...
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844 views

Inductance and Capacitance of wire near ground plane

I'm stuck on the following question and would greatly appreciate any help: A lossless transmission line is formed by a wire of radius a placed in vacuum a distance d above an infinite conducting ...
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317 views

Potential energy on a spherical capacitor

I have been having some trouble understanding the storage of energy inside a spherical capacitor composed of two concentric spherical shells where the inside shell has radius $a$ and charge $2q$, ...
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31 views

Designing capacitor or resistor systems where capacitor or resistor can bear limited voltage

A capacitance of $2\ \mu F$ is required in an electrical circuit across a potential difference of $1.0\ kV$. A large number of $1\ \mu F$ capacitors are available which can withstand a potential ...
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206 views

LC circuit problem

I am currently working on a LC circuit problem where there were given this question that I couldn't understand which is : theoretically justify the shape of the curve (the spring curve) by ...
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1answer
88 views

Discharge time of a mile long capacitor?

I have a mile long parallel plate capacitor AB. It may be taken to be two parallel conducting wire with rectangular cross sections and the wires are close to each other forming the capacitor. The ...
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2answers
678 views

Force on plate of parallel plate capacitor with dielectric

If we have a parallel plate capacitor whose charge is +Q and the polarization charge as Qp as shown in the figure.. then while finding the force acting on the left plate of the capacitor for instance,...
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215 views

How conductive must be capacitor plates?

So from equations I see that a capacitors capacitance increases with area of conductive plates and dielectrical value of dielectric between the plates. It also increases with decrease of distance ...
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85 views

Safety in ultracapacitor discharge regarding possible effects of induced voltages

Problem I am trying to analyze the safety of two experiments involving ultracapacitor short-circuit discharges. In the first experiment one has a discharge of a $0.45 \,\mathrm{F}$ capacitor with ...
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3answers
106 views

What is the total energy stored in the capacitors? Shouldn't the repulsive potential energy stored be included?

Is there the repulsive energy stored in the capacitors or that energy is already included in the conventional calculation of the stored capacitor energy?
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143 views

The effect of the value of capacitance in relation to the load resistance of a single capacitor in smoothing

I can't find a good explanation about: The effect of the value of capacitance in relation to the load resistance of a single capacitor in smoothing. I think it has to do with the following formula:...
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2k views

Which Direction does current flow?

Summary: To simplify, I made the voltage equal to difference in charge: V = Q1 - Q2. If you stack the voltage, current should flow counter-clockwise If you look at the individual charges, current ...
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1answer
84 views

Basic question about using potential divider to limit capacitor charging voltage

This is for a DIY project I'm working on. I know I could just monitor the charging process and unplug before the capacitor blows, or get a more suitable power supply, but it just so happens that I ...
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15 views

How does a super capacitor supply extra energy to an external circuit if the electrolyte doesn't go anywhere

In a super capacitor there is a double layer effect due to charged ions moving into layers. But unlike the electrons in conventional capacitors which line up on a conductive plate and are free to move ...
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2answers
3k views

Redistribution of charges when capacitors are connected in series

This question is asked before but I didn't get the answers It is known that when 2 unequally charged capacitors are connected in parallel then the charges redistribute themselves till the voltage ...
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60 views

Regarding the zero internal electric field in a conductor (electrostatic case)

Let's say we have a homogenous electric field in the $z$-direction. For computational simplicity let's say we have a thin sheet of metal covering entire the $x$-$y$ plane. The answer here is straight ...
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256 views

Circuit with capacitor and battery- why same voltage?

If we connect a capacitor and a battery in the same circuit, what makes the charge move until the voltage on the capacitor is the same as voltage on battery?
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101 views

Minus sign in analyzing RC with changing emf circuit?

I'm learning electromagnetism from Purcell's book. He say that if we have the following circuit: $$-\frac QC + RI = \mathcal E_0\cos\omega t~,\quad I = -\frac{\mathrm dQ}{\mathrm dt} $$ The ...
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39 views

Where will the charge be stored in this capacitor?

A capacitor whose charged plate is hemispherical,concave side is facing each other then will the charge be stored on concave surface like all other capacitors(i.e. parallel plate,cylindrical etc.) or ...
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1answer
49 views

How, if at all, does the behavior of a parallel plate capacitor change in the presence of a magnetic field?

I'm an AP physics student curious about magnetism and my teacher couldn't answer this question. We already learned about velocity selectors, so I know that, when the plates of the capacitor are in the ...
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766 views

Finding Inductance in an AC RLC Circuit?

In the laboratory you find an inductor of unknown inductance $L$ and unknown internal resistance $R$. Using a dc ohmmeter, an ac voltmeter of high impedance, a 1 microfarad capacitor, and a 1000 Hz ...
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1k views

Effect of potential difference on capacitance

I've read multiple threads here discussing the relation between capacitance and potential difference and they have begun to confuse me. I have a homework question about which of the following will ...
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221 views

LCR circuit at resonance

I am studying about the LCR circuit and have a question regarding potential difference across inductor and capacitor. From the thing I have studied I came to know about that potential across inductor ...
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124 views

Physics of the capacitance of an electrolytic capacitor

In explanations about the electrolytic capacitor one often cites the formula $$ C = \epsilon_r \epsilon_0 \frac{A}{d} $$ for the capacitance $C$. Then one says that by enlarging the area $A$ via ...
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71 views

What are the first couple terms of the Taylor series for the evolution of this network of capacitors and resistors?

note: This is a computational problem, and I only need approximate accuracy, so the overall goal is, for a given accuracy and $\Delta t$ to compute the state of the system at $t+\Delta t$ to within ...
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275 views

Capacitors as Energy Wasting?

I am reading a lot of articles about capacitors as the energy storage. Let's consider simple circuitry which contain the battery and capacitor in series. The energy flow from the battery will be $E=\...
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37 views

What size aluminum foil capacitor would power an LED?

Inspired by this video where a $9 \mu F$ capacitor is made from aluminum foil, if I had students put this together in a classroom, one question I would have is what would it take to have this power an ...
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2answers
550 views

Current in discharging capacitor through fixed resistor?

In the textbook I'm using for physics it says that the charge left on the plates of a capacitor after time $t$, that is discharging through a fixed resistor, is $Q=Q_0e^{-t/\tau}$ where $\tau=RC$ is ...
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211 views

What's an intuitive understanding of diffusion capacitance?

Diffusion capacitance often comes up in transistor design. It is one of the two main capacitances you see, the other being the depletion layer capacitance. The depletion layer capacitance (per unit ...
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2answers
700 views

Charged dieletric/conductor in capacitor

It is a standard problem to consider a dielectric or a conductor between the parallel plates of a capacitor. But what happens to capacity, voltage, charge, inserting between the plates of an ideal ...
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207 views

How is derived the relation between capacitances when a $Y-\Delta$ transformation is applied in a capacitors network?

A $Y-\Delta$ transformation can be applied to circuits in order to make an equivalent circuit (but simpler to put in terms of series/parallel devices). Wikipedia and other books show how to deduce the ...
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1k views

What is a boundary condition for capacitors/dielectrics?

I am extremely confused about what boundary conditions are. One minute ago I was solving easy capacitor questions and the next minute I am being asked boundary condition questions and there is no such ...
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1answer
809 views

Cylindrical capacitor with 2 dielectrics

I want to calculate $\vec{E}$ and $\vec{H}$ inside this capacitor: So this would be a cylindrical capacitor but with two different dielectrics in it (they both occupy the same amount of space, excuse ...
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1answer
3k views

In an RLC series circuit on resonance, how can the voltages over the capacitor and the inductor be larger than the source voltage?

Consider an RLC circuit in series, of the form If the source drives the circuit in AC at the resonance frequency $\omega =1/\sqrt{LC}$, the peak-to-peak voltages on the capacitor and the inductor, $$...
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1answer
32 views

If iI have a capacitor connected to a battery can the negative charge be sent to an insulated object

If I have a capacitor permanently connected to a battery, that is lets say setting in a plastic bowl, and then run a wire from the negative of the battery to a non grounded object, say a metal can ...
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3answers
557 views

How does one apply Gauss's Law when dealing with two infinite planes?

If you have two parallel planes with one density of 1 C/m^2 and the other with -1 C/m^2 density and you need to find the electric field at a point in the middle, how do you use Gauss's Law? I drew a ...
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1answer
11 views

Does the dielectric constant changes as the voltage is applied in every dielectric material?

As the voltage is applied at both sides of the dielectric material(ex. front surface +5V and rear surface 0V), the energy is stored in the material, right? I heard it's because the dielectric ...
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1answer
32 views

Is my understanding of the process of charging a capacitor correct?

Suppose, I have a parallel plate capacitor with copper plates $A$ & $B$ connected to a battery. Plate A is connected to the negative terminal of the battery and plate B is connected to the ...
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1answer
46 views

Maximum charge of a capacitor

Suppose we have a capacitor charged with charge $Q1$ Then an electron beam hits the positive plate of the capacitor, thus increasing the charge of the capacitor (the battery will begin to deposit the ...
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Self-energy of a conducting shell when we put some charge inside it

We already know that if we have a conducting sphere with total charge $q$, then the self-energy of the sphere is $\frac{q^2}{8\pi\epsilon R}$, where $R$ is the radius of the sphere. But my question is,...
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Fringe Fields in a Cylindrical Capacitor v/s Parallel Plate Capacitors

I understand that Fringe Fields exist on the edges of a parallel plate capacitor like so: I was trying to figure out if a Cylindrical Capacitor would have fringe fields as well, and how they would ...
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36 views

How does a Capacitor generate a potential difference even after disassembling the Capacitor?

I saw a video of Walter Lewin on YouTube in which he was showing a demonstration on Capacitors. In this demonstration, he gives a charge to the Capacitor, dissembles it and reconstructs the Capacitor. ...
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26 views

Can current flow through a capacitor submerged in electrolytes?

Imagine two flat conducting plates (3 x 3), one as the anode and the other as the cathode, submerged into electrolytes (e.g. sea water) and a DC current is applied to this apparatus. Could current ...
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23 views

How does phase angle impact rms Voltage in an RLC Circuit?

I have an RLC Circuit set up, with a 12Ω Resistor (though the internal resistance of the entire circuit is an additional - approximate - 140Ω), 300 mH inductor, and 100 µF capacitor. There are ...