Questions tagged [capacitance]

The ability of an object to store electric charge.

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

Determining the relationship between plate separation distance and capacitance experimentally

On a lab I recently did, I measured the capacitance between aluminium foils over a range of distances. One of the subsequent questions was to determine the function that best describes the ...
0
votes
1answer
28 views

Charge stored in a capacitor with dielectric when relative permittivity varies

Suppose the relative permittivity of the dielectric in an uncharged capacitor of capacitance C varies with the voltage applied, e.g. k=xV where x has dimensions of V^-1 (After this capacitor is given ...
0
votes
1answer
53 views

Paradox on setting up charges on capacitors

Staring with facts, 1)For a current to flow there must be a closed loop. 2)For a capacitor to be charged there must be a potential difference across it, 3)And obviously a charge must be transferred ...
0
votes
0answers
20 views

Potential and work across capacitor-battery circuit

Suppose, we have a simple capacitor/battery setup like that shown below. The battery is used to charge up the capacitor. After the capacitor is charged, there will be equilibrium, the field of the ...
0
votes
1answer
43 views

Why does the charge required on each plate of a capacitor to maintain a certain voltage decrease with the distance between the plates?

The $Q$ charge and the voltage $V$ of a capacitor are linked by $$Q=C\times V$$ For a parallel plate capacitor $C\propto \frac{1}{d}$. This implies for a given voltage $V$ between the plates, the ...
0
votes
1answer
50 views

Why is the information of a time delay missing in formulae of voltage drop across elements when we emulate DC with an AC voltage supply?

In an AC circuit, the reactance of capacitive and inductive elements are determined by the frequency of the AC signal. When we try to emulate DC analysis by putting $\omega$ = 0 , the capacitive ...
0
votes
1answer
118 views

LCR circuit (AC source) potential difference across capacitor

For a LCR circuit connected to AC source of emf$$E= e\sin(ωt)$$ and let the current in LCR circuit be I then $$I=i*\sin(ωt+Φ)$$ then it is given that potential drop across the capacitor is V.ie$$V=-...
0
votes
1answer
22 views

Electric field in capacitor arrangement with different dielectric media

Please consider the following arrangement of infinitely extended charged plates. In z-direction the system also extends to infinity. The charged plate in the middle of the figure is 2x negatively ...
0
votes
1answer
69 views

Charges on conductor

So i was reading an answer to question Why are the two outer charge densities on a system of parallel charged plates identical? Points that I didn't understand that how come -Q1+x charge can get ...
0
votes
0answers
44 views

Connecting one lead of capacitor to a certain charged object (to get a potential difference)

Setup-A charged sphere , connected to one plate of capacitor , other lead of capacitor is free. Question-Will the capacitor plates go through a charge redistribution ? Arguments/Counterarguments-I ...
0
votes
2answers
106 views

Impedance of an LCR circuit

So I am trying to understand how to find the impedance of the parallel LC component of this filter circuit. I am given that the transfer function $\mathbf{T}_C = \dfrac{\mathbf{V}_{out}}{\mathbf{V}_{...
0
votes
1answer
88 views

Conduction current for parallel-plate capacitor

I am reading Sadiku's Elements of Electromagnetics and here is the proof given to show that conduction current = displacement current for parallel-plate capacitor. Displacement current: \begin{align*}...
0
votes
0answers
85 views

Proper utilization of Ampere’s Law

I am tasked with finding the magnetic field due to a bus bar, which seems to have the exact same set up as Problem 7.62 in the fourth edition of Griffiths' textbook on Electrodynamics. To which I ...
0
votes
1answer
28 views

capacitor and electrostatic field

Is there any electrostatic field around the leads of a charged capacitor? Let's take just the negative one. If I take a piece of tissue and put close to that terminal it will attract or repel the ...
0
votes
0answers
75 views

Derive the formula for a capacitive voltage divider?

I've seen the derivation for a resistive voltage divider, Vout = Vin * R2/ (R1 + R2). For a capacitive divider, Vout is reported as Vout = Vin * C1/ (C1 + C2) - for example see https://en.wikipedia....
0
votes
3answers
50 views

About the capacitance of the capacitor

I would like to ask two questions here , 1. When a capacitor reaches to its maximum limit charge starts leaking and it ionises the air atoms . Well is it true ? As I'm not able to get an convincing ...
0
votes
0answers
271 views

capacitance of cube skeleton

A cube of 12 capacitors is very common problem. find capaciance accross edges we get 12c/7. But lets say we have 8 more capacitors involved now. that is we have capacitors at all sides of cube and ...
0
votes
1answer
75 views

Does an uncharged capacitor in a non uniform electric field have a voltage difference at its terminals?

If an uncharged capacitor was placed in a dc field would there be a voltage difference developed on its terminals related to the different locations of the two surfaces in the voltage field? Would the ...
0
votes
0answers
636 views

Capacitance of spherical capacitor when inner sphere is earthed

Consider the following derivation: (Source: http://www.ncert.nic.in/html/learning_basket/electricity/electricity/electrostatics/inner_sphere.htm) If a charge of $+Q$ coulombs is given to the outer ...
0
votes
0answers
54 views

rotating capacitor question

Imagine a simple setup. I have a copper disc and another copper element held close to the disc at one of it's sides, this element is stationary but the disc is rotating, the part between the disc and ...
0
votes
1answer
30 views

Error of capacitnace measurement using a multimeter

physics stack exchange Many multimeters have a setting for measuring capacitance. The multimeter I have has a precision of four significant figures, or in other words, it returns the value in the ...
0
votes
1answer
79 views

How do multi-meters measure capacitance?

Many multimeters have the ability to measure capacitance along with the ability to measure AC voltage, DC voltage, current, resistance ... The only equations I am aware of that determine capacitance ...
0
votes
0answers
27 views

Why didn't my Capactive Wireless Power Transfer work?

Today I had the delight of setting up a bipolar capactive wireless power transfer (CWPT) circuit for a school experiment. Disappointingly, it did not work. It was set up just like in the diagram ...
0
votes
1answer
61 views

Capacitor, stored energy versus reactive power

When an AC voltage U is put onto a loss less capacitor C the capacitor will require a certain reactive power Q (current 90 degress out of phase with the voltage): $Q=UI = \omega C U^2$ in VAr (Only ...
0
votes
1answer
37 views

Limit charge of electronic–hydraulic analogy of a compartment

I am doing a mathematical model of an hydraulic system and I am using an electronic-hydraulic analogy. Normally a compartment is simulated with a capacitor. But in my system I can apply a big ...
0
votes
2answers
40 views

New charge of a capacitor

How does the load of a charged capacitor vary when placing a dielectric between the plates while keeping the capacitor connected to the battery? If we have a capacitor that we have charged to the ...
0
votes
1answer
525 views

Capacitance of a 2D capacitor

I would like to know how to calculate the capacitance of a 2D capacitor and the derivation of the formula. I have been looking all over the place but could not find an answer to this. Thank you!
0
votes
0answers
1k views

Capacitance of Two Parallel Cylinders

I have some issues with the sign of the solution that I found. The problem is Two cylindrical conductors of radii R, separated by a distance $2d$, are charged with a potential difference $V$. Find ...
0
votes
0answers
163 views

Why doesn't this formula for spherical capacitors in series apply in all cases?

The capacitance for two spherical capacitors (in series) is$$ \large{C~=~\frac{4 \pi\epsilon_0}{\frac{1}{r_{\text{inner}}}+\frac{1}{r_{\text{outer}}}-\frac{2}{d}}}\,,$$ where: $r_{\text{inner}}$ is ...
0
votes
1answer
312 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
38 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
157 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
500 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
69 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
75 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
1answer
157 views

Fully filled capacitors with parallel dielectrics problem

consider that we have two dielectrics inside a capacitor as shown in the picture, let0s consider also that Q is the charge of the capacitor and d the distance between the two plates , the first ...
0
votes
0answers
264 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
960 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
104 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
272 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
344 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
34 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
167 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
121 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
170 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
57 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
37 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
241 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
348 views

Capacitance calculation with numerical methods

For this structure (ellipse conductor covered with circle conductor. between them full of dielectric) I calculated electric field distribution with finite difference (Dirichlet problem for Laplace eq.)...
0
votes
1answer
90 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 ...