Questions tagged [capacitance]

The ability of an object to store electric charge.

240 questions with no upvoted or accepted answers
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8
votes
2answers
746 views

Express Laplace transform of voltage across a capacitor in terms of charge

In Charge Tunneling Rates in Ultrasmall Junctions section 2.1, the authors consider the problem of charge relaxation in a simple circuit shown in Figure A. The implicitly use an assumption made about ...
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1answer
616 views

My fingers are sparking large source of electricity when I touch plastic boards covered with polythene

Still I don't understand why am getting such voltage & it's the same feel that I touched 250 voltage of current. Also when I put two fingers on opposite direction (when I am removing polythene ...
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1answer
459 views

What is capacitance, in general?

In circuit analysis software capacitance can be measured between any two nodes of a circuit or of a multiterminal device. In practical terms we take $C_{ij}$, the capacitance between $i$ and $j$ as ...
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2answers
117 views

Confusion regarding Gauss law and capacitors

In book (Halliday Resnick Krane, 2nd Part, fifth edition), it's written that when you you put some charge in an isolated conductor, then within around $10^{-9}$ seconds the charges all go to the ...
3
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0answers
399 views

non-symmetric spherical capacitor

The figures below illustrate (in cross-sectional view) three separate spherical capacitors: an inner solid conducting sphere is surrounded by a hollow thin conducting shell, concentric with the sphere....
3
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2answers
115 views

Two balls are attached with a very long and thin conducting wire to two conducting plates. How does the capacitor react in this situation?

The question is as follows (taken from a previous exam): Two balls (conductors w/ Radius $R_1$ for left ball ball, $R_2$ for right) are attached with a very long and thin conducting wire to two ...
2
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0answers
55 views

In an $RC$ Circuit, when polarity of a battery is reversed, how much energy is dissipated into heat?

https://ibb.co/tPL02dZ In the figure, a $ 20 nF $ capacitor is connected in parallel across a $ 30 nF $ capacitor. There are $2 $ resistors of $10 Ω$ connected in series with the capacitors. A ...
2
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1answer
80 views

How Are Electromagnetic Waves Produced?

How EM waves are produced say by a capacitor of an LC circuit here if $E$ is increasing in upward direction? My thoughts Thought 1:- If E is increasing E flux is increasing thus B field must be ...
2
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2answers
195 views

Common potential in Capacitors

If two isolated charged capacitors (of different capacitance) are connected in parallel to each other they acquire a common potential. But suppose if i connect positive plate of one capacitor to ...
2
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1answer
51 views

Is it possible to use a capacitor to cool the surrounding medium by pulling its plates apart while remaining connected to the battery?

Considering a parallel plate capacitor connected to a battery. If plates are pulled apart heat is not produced. But the battery is absorbing energy as it gets charged. So heat is absorbed. If this is ...
2
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1answer
105 views

Dual finite parallel disk capacitor; estimating mathematically that the potential or field or distribution is nearly uniform from first principles

Working through Purcell. In particular, doing my best to put everything on a firm footing, mathematically, so that I can understand it. But, I have struggled all week in establishing from first ...
2
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2answers
198 views

Is the charge on the plates of a parallel plate capacitor induced charge?

My question is- Is the charge on the plates of a parallel plate capacitor induced charge? Imagine two plates of the capacitor have $+q$ and $-q$ charges on it. Basically, what I want to know is ...
2
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0answers
180 views

In series RLC circuit, does decreasing the capacitance value really make the circuit more capacitive circuit?

This seems very counter intuitive to me. How can decreasing the capacitance value make the circuit more capacitive ? The math tells me so : If $C$ decreases then $X_c = \dfrac{1}{\omega C}$ ...
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0answers
350 views

What is Capacitance for a Spherical Shell pair?

Consider three Scenarios : 1) In this case , we are Calculating $$\frac{d(Q_b)}{d( \triangle Vab)} $$ 2) In this case , we are Calculating $$\frac{d(Q_a)}{d( \triangle Vab)}$$ 3) In this ...
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0answers
2k views

Combination of dielectrics in capacitor

For figure 2 in the above diagram, I derived the following equation: $$\\E_{o}= E_{1} + E_{2}$$ Where $\\E_1$ and $\\E_2$ are the net electric fields or dielectric 1 and 2, respectively (i.e., $\\E_{...
2
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1answer
132 views

Spherical capacitors and their discharge rates?

Imagine that you have 2 small metal spheres (about $2\mathrm{cm}$ diameter), which are set $x\mathrm{mm}$'s apart from each other, with only air in between. You start to charge the spheres, one ...
2
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0answers
82 views

Is there a theoretical limit for the Dielectric Constant

If we're being pedantic, it's a Dielectric Tensor, and I know that it changes with both temperature and frequency, but the question remains... How would one calculate the theoretical maximum ...
2
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0answers
109 views

Why do ceramic magnets work on touch screens?

I know how our touch screens work by sensing changes in voltage with capacitors, and then pinpointing our fingers location. But recently I was playing with a ceramic magnet on my phone. As I took ...
2
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1answer
90 views

Tangential Current of plates in charging capacitor (Function of x)

Suppose we have a capacitor which is charging with applied voltage $(V(t)).$ I want to know what the surface current is which is shown in figure. I know the continuity equation says the current of ...
2
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2answers
358 views

Different charges of plates of parallel plate capacitor

Suppose the plates of a parallel plate capacitor have charges +2Q and -Q initially. Then if they are connected with a battery of emf V what will be the charge distribution on the plates of capacitor? ...
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0answers
36 views

Scale-covariant decomposition of capacitance

I'm wondering if there is any good insight of how to evaluate a given capacitive geometry in such a way that it would be expressed as a function that depends only on two components: as a geometric ...
2
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3answers
495 views

Capacitor and Pith Ball experiment

Suppose I first charge a capacitor so that one plate is positively charged and another negatively. Now I remove the charging source and ground only one of the terminals say negative terminal, will ...
2
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0answers
421 views

Circumference measurement using a capacitive sensor

I have a question which I hope someone in here can help me answer. Background: I’m building a device where I intend to use a stretchable capacitive sensor to define the radius change of an object. ...
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0answers
1k views

Absolute permittivity and permeability of free space

I'm reading about the propagation of EM waves in vacuum. We define the wave equation using two constants: $\epsilon_0$ and $\mu_0$. Of course they are absolute permittivity and absolute permeability ...
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0answers
494 views

Calculating Electric Field from a Potential Difference w/o Charge

So here is my homework question: Two long cylindrical shells of metal (radii $r_1$ and $r_2$, $r_2 > r_1$) are arranged coaxially. The plates are maintained at the potential difference $\Delta\...
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0answers
737 views

Dielectric in Parallel Plate Capacitor

Given a parallel plate capacitor of width $w$, length $l$, with a dielectric moving along the length $l$. Let the dielectric be from $x$ onwards. The capacitance will be $\frac{w \epsilon_0}{d} (\...
2
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1answer
130 views

Effect of Motion on Capacitors

What will happen if a capacitor is accelerated or rotated very very fast? Will its capacitance decrease? Will one of the plates be able to hold the electrons which is providing the Potential ...
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0answers
19 views

Charge density inside dielectric with conductivity

Consider the figures I and II , they consist of similar circuits with identical batteries. There are two different slabs connected in the circuit, both are geometrically identical and have the same ...
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1answer
33 views

How does RF communication between electronic circuit elements affect the circuit?

The other day, a friend and I were looking at a simple resistor-capacitor-inductor circuit. As we were looking at the circuit, he mentioned that the capacitors and inductors "talked" to each ...
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1answer
36 views

Is it necessary that a capacitor stores charge?

Is it necessary that a capacitor storage charge? I am a little bit confused. For example: if I take two concentric conducting shells and a positive point charge at the centre. Both the surfaces (outer ...
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0answers
39 views

Crossover filter gives weird results

I was analyzing results of an experiment on a crossover filter and I was trying to take into consideration the parasitic resistance of the inductor L (called $R_L$). I know the theoretical crossover ...
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0answers
21 views

Why does single electron Coulomb blockade charging use $Q^2/2C$?

Classically stored energy of a capacitor is $\frac{Q^2}{2C}$. However, the difference in energy when a single electron travels across the gates should be $qV$ But in couloumb blockade calculations, ...
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1answer
134 views

Capacitance of spherical capacitor when inner surface of outer sphere is earthed

Let there be two concentric shells in which the outer sphere contains charge Q1 and inner sphere contains charge Q.Capacitance of spherical capacitor when the inner surface of the outer sphere is ...
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1answer
46 views

Why is the field inside a capacitor not the sum of the field produced by each plate?

In this answer by David Z, we can read, When discussing an ideal parallel-plate capacitor, $\sigma$ usually denotes the area charge density of the plate as a whole - that is, the total charge on the ...
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2answers
51 views

Attenuation of a signal

Suppose that I have a wire between two terminals and I want to send a high frequency ($f$) signal from one to another. Is the inductance and capacitance per unit of distance enough to calculate the ...
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0answers
35 views

The force needed to move air for electrostatic speakers/headphones

I am trying to determine what force is needed for the membrane of an electrostatic speaker (headphones, etc) to move the air at a particular frequency. I know that the formula for the force acting on ...
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0answers
10 views

Inner Sphere of Capacitor is Grounded versus Rested on Insulated Stand

My Question is about understanding the difference in Charge Distribution in a Spherical Capacitor in 2 Scenarios Here are the details of the Problem scenarios :- If we have a Spherical Capacitor ...
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0answers
20 views

Charge distribution and potential changes on earthing for conductors placed close to each other?

Suppose we have two conducting plates with charges $2Q$ and $3Q$ placed close to each other (ignore edge effects for simplicity). It is clear that when the switch is open, the charge distribution is ...
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1answer
52 views

Capacitor problem: What's wrong with this?

The capacitor shown contains 3 different dielectric material $\epsilon_1,\epsilon_2,\epsilon_3$ between the top and bottom metallic plates on which lie teh points $A$ and $B$ as shown. The electric ...
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0answers
24 views

A relationship between parallel plate capcatior's capacitance & it's spacing distance

In my experiment class, I measured a curve between the parallel plate capacitor's capacitance and it's spacing distance. But the result is not very similar to expectation - despite the spacing ...
1
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1answer
171 views

Repulsive force from charge accumulation in a capacitor plate?

During a charged state of a capacitor (Regardless of the type of capacitor), Simple parallel plate: .png Parallel plate with dielectric material in the gap: ]3 Supercapacitor: How is the ...
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0answers
65 views

Calculating the self capacitance of a rectangular electrode with a dielectric on one side

I am trying to derive an expression for the capacitance of a rectangular electrode with a dielectric material of thickness $t$ and relative permittivity $\epsilon_r$ in contact with one side, sized ...
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0answers
16 views

Effects generated from a supercapacitor placed in a time varying external magnetic field?

The diagram above, showcases the simple outlook of a supercapacitor's interior and combining it with a full circuit loop. If an exterior magnetic field is introduced in all the operating states of a ...
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0answers
24 views

Metal Oxide Semiconductor (MOS) Capacitor strong inversion

Why the electron bands in the Body of the MOS capacitor do not bend much futher after the threshold voltage is applied? What stops them from doing it? For reference Modern Semiconductor Devices for IC ...
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0answers
123 views

How does charge flow (directions) from capacitors in this question?

A circuit is connected as shown in the figure with the switch S open. When the switch is closed the total amount of charge that flows from $Y$ to $X$ is? (A) $0$ (B) 54$\mu$C (C) 27 $\mu$C (D) 81 $...
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0answers
49 views

Change in temperature of dielectric when capacitor is charged and discharged

Suppose I have a capacitor with a dielectric between its plates. Intially the temperature of dielectric is $T_{-1}$. The capacitor is fully charged and the temperature of dielectric is noted.. say, $...
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3answers
208 views

RC circuit discharge while being connected to a battery?

I am facing a conceptual problem in analyzing the following situation which was part of a physics exam: A series RC circuit with $R = 200k \Omega$ and $C = 10 \mu F$ is connected to a 5V battery and ...
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2answers
396 views

Adding a capacitor in parallel improves power factor of an inductive circuit?

I know that to reduce power loss during transmission, we require a power factor as close to one as possible. This can be done by making $Z$ tend to $R$ which can be done by increasing $X_c$ such that ...
1
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1answer
42 views

Resolve The Envelope Detector Circuit

I was working on a little project and I was wondering if the envelope detector circuit could be resolved analytically. Let me explain. The circuit is the one shown above, I know the values of $C$, $R$...
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0answers
17 views

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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