The ability of an object to store electric charge.

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3answers
868 views

How can I find the potential created by spherical capacitor with dielectric material?

If we have a spherical capacitor with inner radius or r1 and outer radius of r2, with charges (+/-)q on them and there is a dielectric material (with constant e) in between them with. What kind of a ...
0
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3answers
73 views

Can the potential difference produced in Van De Graff generator used to generate electric current?

If this machine can build up high voltages of order of millions of volts, can we use this volt the generate current of electrons? The building up of potential difference can result in electric field. ...
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2answers
49 views

Why does electrical impedance have as many parameters as it has?

The impedance of a circuit is written: $$ Z(R,L,C,f) = R + j ( 2 \pi f L - \frac{1}{2 \pi f C} ). $$ What is the line of thinking that frequency, resistance, capacitance, and inductance are the only ...
0
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2answers
131 views

Two capacitor plates with equal positive charges $q$

I read in a book that if both the plates of a parallel plate capacitor are given equal positive charges $q$, then the charges on the facing surfaces will be zero and the charge on the outer surfaces ...
0
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2answers
49 views

Charging a spherical capacitance

How could one charge a spherical capacitor with a battery or any other emf source?
3
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1answer
102 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 ...
1
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1answer
39 views

Variation of Peak Current and Peak Voltage with Capacitance in an AC circuit

The relation of Peak current, Peak voltage and Capacitive Reactance in Alternating Current is given by: $$i_m=\frac{v_m}{X_c}$$ and $$X_c=\frac{1}{C\omega }$$ So if we have a circuit with a ...
0
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1answer
63 views

Cylindrical capacitor in an electric circuit

I've come across a tricky question and would appreciate some hints or explanations as to why the given solution is the way it is. The question reads as follows: A coaxial cable consists of a wire ...
0
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1answer
49 views

Capacitance of spherical capacitor when earthed

The capacitance of a spherical capacitor is given by $$C=\frac{4\pi \varepsilon_{0}}{\left ( \frac{1}{a}-\frac{1}{b} \right )}$$ How can I find out the capacitance of the capacitor when The ...
0
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1answer
54 views

What does an increased time constant of a capacitor do?

If a capacitor is being charged to any voltage, what effect would increasing the time constant have on it and if a graph of Charge Q/Time T was plotted to give a positive decreasing gradient, how ...
0
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1answer
37 views

What does “Receptor” convention refers to in RC circuits?

my question is How can we choose the convention in a circuit and what does it refer to ? Especially for a Capacitor I hear the terms "passive sign convention..." "receptor convention ..." "generator ...
0
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1answer
191 views

Finding the voltage of the circuit?

Capacitor 3 in Figure (a) is a variable capacitor (its capacitance C3 can be varied). Figure (b) gives the electric potential V1 across capacitor 1 versus C3. The horizontal scale is set by C3s = 20 ...
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1answer
24 views

Potential of 2 parallel plates

How can I write down a potential of 2 parallel plates (area $A$) with charge $+Q$, $-Q$ such that V(inf)=0 and V(in) is what I would expect, $Ed = Qd/A\epsilon_0$. Do I have to write a discontinuous ...
0
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1answer
69 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 ...
0
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1answer
43 views

Capacitance per unit charge of three long rods, two of which are connected

Suppose we have three very long rods, each with diameter $a$, placed so that their "centers" form an equilateral triangle, with sided of length $d$. Two of the wires are connected with a thin wire ( ...
0
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1answer
51 views

Discharging capacitor

When the capacitor is fully charged and the switch as it B, how can we apply KVL at that loop to reduce the equation to (-IR)? Why is it negative? At time = 0 is the current not zero? And it will ...
0
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1answer
53 views

Negative charge on capacitor, Kirchoff differential equation with step function

I'm solving a differential equation of the form $$200q'+\frac{200}{3}q=3U_o-6U_6+3U_{12}$$ Where $U$ is the Heaviside step function. $q(0)=0 [Coulombs] $ After solving it, I get that at time $t=18$ ...
0
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1answer
1k views

Capacitor charging, work done by battery on changing polarity

A uncharged capacitor $C$ is connected to a battery with potential $V$. It becomes fully charged and has a charge $Q=CV$ stored on it. Now the polarity of the battery is reversed. The capacitor will ...
-1
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1answer
899 views

Capacitance of two non parallel plates

What is the formula for capacitance of two non parallel plates at an angle with each other?If the plates were parallel then the value can be calculated as (PermittivityX area of one plate)/distance ...
8
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0answers
157 views

Are there analogs to resistance, inductance, capacitance, and memristance connecting the weak force to electromagnetism?

A question was asked over at EE.SE recently which I tried to answer, but much of my answer was speculative. I'm hoping someone here can help my ignorance. In electronics design, there are four ...
2
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0answers
22 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. ...
2
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0answers
268 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 ...
2
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0answers
329 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 ...
2
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0answers
496 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} ...
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0answers
58 views

How is the formula for the capacitance of a parallel plate capacitor derived?

I have seen in I.E. Irodov that if the permittivity is given as $\epsilon$ then we can find the capacitance as $$C = \frac{\epsilon A}{d}$$ but I wonder whether it is dimensionally correct or not and ...
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0answers
37 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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0answers
30 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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0answers
143 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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0answers
578 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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0answers
25 views

Where can I find a good theoretical treatment of conductor shielding?

Suppose one has three current carrying cylinders lying on the same plane. Some of the electric field of the first conductor ends up on the second conductor, which creates capacitance C12. But also ...
0
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0answers
32 views

Maximum current in LC Circuits

Two capacitors of capacitance $C$ and $3C$ are charged to potential difference $V_o$ and $2V_o$ respectively and connected to an inductor, all three in series. Now the switch S is closed. Find the ...
0
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0answers
28 views

Non-parallel-plate Capacitor

Imagine you start with a parallel plate capacitor with square plates of side $s$ and gap $p$. Turning one of the plates slightly results in a small increase and decrease in gap separation $d$ at the ...
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0answers
10 views

Image charges for currents?

I am struggling to get my head around a problem involving creating a transmission line using a wire of radius $a$ in a vacuum a distance $d$ above an infinite grounded plate ($d \gg a$). I wish to ...
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24 views

Initial current, RC Circuit

The task goes like this: The voltage between the points A and B, in the circuit diagram below, is 100 V. What's the initial current through the resistor when we close the switch S? (Other components - ...
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0answers
27 views

How to calculate the capacity of an electroscope out of the geometry and why is it independent on the pointer deflection?

How can one calculate the capacity of an elektroscope like the following from the geometry of the setup? How does this formula implies that the capacity does not (approximatly) depend on the ...
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0answers
19 views

Designing a capacitor and electrical double layer capacitor

Hello! based on the image above, I am wondering if my assumptions are correct that i can make a capacitor using this design (1) and (2) are "infinitely" long layers (1) layer is made up of same ...
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0answers
19 views

Back force after capacitor is discharged

You have a mechanical hand crank generator connected to a capacitor. You charge the capacitor by cranking it (you obviously have a back current as you crank it so it is difficult to crank). At a ...
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0answers
15 views

Current flow in a polarized capcitor

What is a polarized capacitor? I have learned that in a polarized capacitor, the negative lead must be connected to the negative terminal of the battery and so the positive. But my doubt is that if ...
0
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0answers
40 views

Can Van Allen Radiation belts act as a capacitor?

There are two Van Allen Belts at rougly 5000Km and 17000Km from the surface of the Earth each of them containing majority of one of the charges electrons and protons). Can these belts like a ...
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0answers
59 views

Capacitance per unit length of a system containing uniformly charged rod and and infinite charged plate

Suppose we have an infinite plane, and a uniformly charged rod of radius $a$ and linear charge density $\alpha$, parallel to the plane and at distance $d$ from it. Net charge of the plane is $0$. Rod ...
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0answers
129 views

The force acting on a plate of a parallel capacitor

How can you prove (using high-school-knowledge) that the force which acts on one plate of a parallel capacitor is equal $F = \frac{E \cdot Q}{2}$ Where $E = \frac{U}{d}$ is the magnitude of the ...
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0answers
63 views

capacitors - Square circuit of two capacitors charging in a changing magnetic field

I've been studying capacitors and DC circuits, and I received this question as part of my homework: The above circuit is a square circuit with side a. E and F are the midpoints of AB and CD ...
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0answers
30 views

The physics behind capacitive touch sensing

Can someone explain the mechanism of capacitive touch sensing? According to http://www.planetanalog.com/document.asp?doc_id=527410&site=planetanalog&print=yes, it mentions "fringing fields", ...
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0answers
94 views

Energy of moving capacitor

On the following link were a discussion about energy in capacitor moving parallel to its field: Where's the energy in a boosted capacitor? My question is what happen if capacitor is moving ...
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0answers
46 views

Capacitance changes by a factor of 3 or 9?

This is an example problem with solution in a book I am reading on electrostatics. "We have two square parallel plate capacitors with length $a$ and separation $d$ with $d<<a$. If we triple ...
0
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0answers
64 views

How can a paper battery behave like a capacitor?

I was trying to understand how paper batteries work and came across some explanations saying that the paper battery can also behave like a supercapacitor on account of its ability to discharge and to ...
0
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0answers
97 views

Does the Fringe effect occur in capacitors in the interdigitated form?

I am currently doing my undergrad dissertation on graphene supercapacitors. I have read that the fringe effect is a well established phenomenon on parallel plate capacitors, but does it also occur in ...
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0answers
62 views

Electric Potential Change

Imagine we have a conductor in the shape of a sphere with charge $Q$ on it. The conductor is not grounded. There is an associated potential $V=\frac{Q}{4\pi\epsilon_0 R}$ at and in the sphere, where ...
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0answers
96 views

What is the electrical field of a capacitor plate as a charge approaches

The electrical field for a charge density $\varrho(r)$ is $${\bf E}({\bf r})=\frac{1}{4\pi\varepsilon_0}\int \varrho({\bf r}')\frac{{\bf r}-{\bf r}'}{\hspace{.1cm }|{\bf r}-{\bf r}'|^3} \mathrm ...
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0answers
17 views

Conductor in electrostatic equilibrium

Consider the following capacitor: The upper conductor is charged by $Q$. There's a conductor on the middle with thickness $e$. The lower conductor is connected to the ground. All of them have area ...