Questions tagged [capacitance]

The ability of an object to store electric charge.

263 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
0
votes
1answer
355 views

Insertion of current carrying metal sheet between the plates of parallel plate capacitor

A parallel plate capacitor with area of plates A and distance between them d is charged with Voltage V1. A metal sheet carrying current is inserted between the sheets. How does the system change? What'...
0
votes
1answer
40 views

How can a conductor plate stay neutral when we force it to be charged?

At the beginning of this video "Capacitors and Capacitance: Capacitor physics and circuit operation" Let say, blue particles be negative charges. In the video, it is claimed that If we push electrons ...
0
votes
1answer
204 views

RC constant in a coaxial cable

i have a problem with understanding a certain aspect of calculating the RC constant in a coaxial cable. Given the reistance in the inner wire, and the outer wire, and given the capacitance. These ...
0
votes
2answers
555 views

Current in a RC circuit

In order to find current in an RC circuit, resistance of only the resistor is considered i.e. $I_\text{resistor} = V_\text{resistor} / R$. Why is the reactance of the capacitor not considered? The ...
0
votes
0answers
75 views

Partial discharge of capacitors - can it be engineered to give a desired, continuous output?

Don't know anything about physics. I expect to be ignored or told to go somewhere else. My question is on converting energy stored in a capacitor by engineering controlled partial discharge (leakage,...
0
votes
1answer
79 views

LC linear circuits problem with phasors

How would you approach this problem: I went about it by first converting everything to its phasor values, then applying the principle of superposition. According to my calculations: $\omega = 2, Z_L=...
0
votes
2answers
166 views

Showing that an electric field is uniform

This question might be a bit strange. Two charged plates will have a uniform electric field between them. Is there a relatively simple way to show that the electric field between them is constant? ...
0
votes
0answers
282 views

Capacitors, net charge and the Coulomb force

So, my understanding is that the Coulomb force, k(Q1*Q2)/r^2, produces a very large result for force (about 9*10^9 Newtons for two Coulombs of charge at a distance of a meter from each other), but ...
0
votes
1answer
1k views

Diode-Resistor-Capacitor Circuit Equations

So I took the time to measure the current dependency on voltage of a diode I have. I applied an exponential fit to it, and have a pretty reliable equation (within 1%). I'm interested in how a diode-...
0
votes
0answers
105 views

Why, intuitively, does a capacitor create current?

Suppose we have a planar capacitor connected to a closed wire. If the capacitor is charged, we know that the stored energy will be dumped in the form of current, electrons flowing from the negative ...
0
votes
2answers
304 views

Electrostatics - Potential near conductor using Kelvins method of image charge

As the figure shows, I have a 2D image of a conductor seen from the front. It is located a height, h1, above a grounded plane of infinite area. The conductor has a voltage, Vc, as shown. Around the ...
0
votes
1answer
364 views

Charge distribution in series combination of capacitors

its a normal series combination of capacitors,only the inner plates are placed differently,one in the beginning and one in the middle,will it not alter the charge distribution ? that is if we will ...
0
votes
1answer
36 views

Why is it required to consider distance of seperation in calculating the electric field of a parallel plate capacitor?

In my textbook, it is said: "Since $d$ is much smaller than the linear dimension of the plates ($d^2 << A$), we can use the result on electric field by an infinite plane sheet of uniform surface ...
0
votes
1answer
174 views

Predicting voltages in RLC series circuits from AC source: differences in order?

Hoping this isn't too homework-like, but I'm missing some sort of concept here. Doing a lab, and I have to use previous data to predict the voltage across the 2nd and 3rd elements (e.g. order is LCR, ...
0
votes
2answers
143 views

Capacitor Discharging through a fixed resistor

When a capacitor discharges, the pd across it goes from V0 to 0 in a given time. But when you look at the pd across the fixed resistor, this too decreases from V0 to 0. So we can say Vcapacitor=...
0
votes
1answer
255 views

Gain as a Function of Frequency (RC High Pass Filters)

I configured a simple series RC circuit. Across the circuit I have placed the terminals of a sinusoidal AC voltage source (I'm using my phone as a function generator). My goal has been to measure the ...
0
votes
1answer
63 views

How to compare performance of different supercapacitors

I've been reading a research review paper about supercapacitors (SC) http://pubs.rsc.org/en/content/articlehtml/2015/ee/c4ee03229b I want to compare the performance of SCs based on their ...
0
votes
1answer
43 views

Calculating electric field in a dielectric

Why the electric field calculated in a dielectric is equal to the uniform charge density per unit area divided by epsilon-0 (which is the permitivity in space) shouldn't it be divided by another ...
0
votes
0answers
261 views

Charge on a charged capacitor as a function of time

Suppose I charge a circular parallel plate capacitor (capacity $C$, filled with a dielectric substance of electrical permittivity $\epsilon$ and conductivity $g$ ) with potential $V$ and then remove ...
0
votes
1answer
100 views

Can you assign a capacitance to a polarized sphere?

Many times in EM I've seen the classic problem of solving for the fields of a uniformly polarized sphere. Moreover, electrical engineers love giving the problem "solve for the capacitance of a ...
0
votes
1answer
36 views

Wouldn't extra surface area from a thicker active material layer in super capacitors be more important than minimizing the gap distance

Capacitance is proportional area, and inversely proportional to gap distance. I've read all over the internet that you need to make capacitors have as small a gap distance as possible, but I wonder if ...
0
votes
0answers
132 views

Charge density on a capacitor plate

Is charge uniformly distributed on a capacitor plate? For a conductor, charge density is more at sharp ends. So, shouldn't charge density be more on the corners of the plate?
0
votes
1answer
82 views

If you would replace ITO, would it ideally have a lower or higher relative permittivity?

ITO is used as the conductive layer in a touchscreen. If you would replace ITO in a capacitive touchscreen, would it ideally have a lower or high relative permittivity? The relative permittivity (...
0
votes
0answers
126 views

Calculating Electrostatic Energy from Capacitance Matrix

Let's say I have two spherical conductors and I put some charge on each. As I understand it, the electrostatic energy $W$ in the fields will be equal to $$W = \frac{1}{2}C_{11}V_1^2 + \frac{1}{2}C_{22}...
0
votes
0answers
43 views

How to know the values of $R$ and $L$?

Yo there! I have a RL circuit in the arrange showed in the image. Ok, the trick is how can determine the values of the components based on the graphics of a step and impulse response, I detail the ...
0
votes
1answer
60 views

What causes the double layer in supercapacitors?

I know that the potentials on the supercapacitor electrodes will attract opposite charges in the electrolyte thereby forming a double layer. This double layer acts as an insulator to prevent current ...
0
votes
0answers
83 views

Can a statically charged object flying in an airplane float?

Lets say you are flying in a plane headed due west at 1000 km/h (278 m/s) with an altitude of 10km. According to http://www.ngdc.noaa.gov/geomag-web/#igrfwmm, at 10km altitude, Earth's magnetic field ...
0
votes
1answer
441 views

Electric field created by a battery

If I create an electric field using a battery between two parallel plates and leave the battery connected, will the electric field always exist for as long as the battery lasts, including normal self ...
0
votes
0answers
426 views

Electrostatic energy of the system

Problem : $(A)$ There are two thin concentric metallic shells of radius $a$ and $b$ $(b>a)$. Inner shell carries a total charge $Q$ and the outer shell carried a total charge $–Q$. Calculate the ...
0
votes
1answer
22 views

Relyance of plate distance on the capacitor equation

I am studying capacitors and i cannot seem to understand why the increase/ decrease in voltage and distance between the plates would affect the capacitor's abillity to store charge. Can anyone help??
0
votes
0answers
64 views

Is it possible to get an analytic expression of the capacitance for this geometry?

Here is the geometry I'm talking about: Assume the red rectangle is at some constant potential V, like 10 Volts, and the blue is at ground. We can assume that the rectangles extend infinitely (to the ...
0
votes
0answers
57 views

May the total charge in a supercapacitor be different using unipolar and bipolar voltage power supply?

Consider a supercapacitor where a Helmoltz double layer is formed at each of the 2 electrodes, which is like having 2 capacitors mounted in series, but with different polarities. The total charge at ...
0
votes
1answer
879 views

Principle of capacitor

It is said that second conductor reduces the potential of fist conductor and hence increases charge taking ability of first conductor My confusion... As per my limited knowledge it is electric field ...
0
votes
1answer
92 views

doubt from capacitance and capacitors

Can a charged capacitor mathematically be represented as uncharged capacitor connected in series with battery of opposing emf ? Please explain with an example
0
votes
1answer
52 views

Arms of Parallal Plate Capacitor

In case if Parallel Plate Capacitors, is it necessary for the two plates to be equal in length? If yes why? And if they were not equal, what would be the problem?
0
votes
0answers
101 views

Why should we use good conductors as electrodes of a capacitor?

I was asked if and why why should the electrodes of a capacitor should be good electrical conductors. It seemed obvious to me that if I want to form a Helmholtz double layer (because that's what ...
0
votes
1answer
811 views

How to compute the charge as a function of time in a simple $CL$ circuit?

I am trying to compute $q(t)$ in a series circuit consisting of a capacitor of plate charges $q_0$ and $-q_0$ and an inductor. The switch is closed at time $t=0$. By Kirchoff's Law, $$\frac{q}{C}+L\...
0
votes
2answers
92 views

How is the capacitor affected?

I know that a capacitor stores electric energy or electric charge and understand how, but I don't understand how the distance and the voltage affects its capacitance (I mean what are the mechanisms ...
0
votes
1answer
202 views

Currents in an isolated metal exposed to an alternating uniform electric field

For example, let's look at a metal sphere between a capacitor's (infinite) plates. Let's run an AC current through the capacitor, resulting in an oscillating electric field. The charges will move in ...
0
votes
1answer
37 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
votes
0answers
60 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 ...
0
votes
1answer
158 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
votes
0answers
132 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 ...
0
votes
0answers
65 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
votes
2answers
83 views

Charging a spherical capacitance

How could one charge a spherical capacitor with a battery or any other emf source?
0
votes
0answers
482 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 ...
0
votes
0answers
132 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 d^3r'....
0
votes
2answers
77 views

Electric field in capacitors

As many of you may know, a capacitor stores energy by means of the electric field crested between the plates of this capacitor, but how is the electric field able to store the energy itself?
0
votes
2answers
188 views

Amount of energy that can be stored from Faraday flashlight / linear alternator?

You'll have to forgive me if this question is either extremely elementary or does not make sense — I am a civil engineer with little E/M physics background beyond high school education. I am working ...
-1
votes
1answer
53 views

Are electric fields constant in the dielectric materials of a parallel plate capacitor?

For every example I've seen this was an assumption I have made. However with this example, I am unsure. Either the electric field is constant through the e1 dielectric meaning e2 and e3 must be equal, ...