# Questions tagged [capacitance]

The ability of an object to store electric charge.

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### Charging a capacitor with a battery

I'm trying to better understand the process of charging a capacitor with a battery. My textbook (the Halliday's Fundamental of Physics) describes this process in these terms: When the circuit [...] ...
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1 vote
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### Capacitance of a System of Two Spheres

To explain more clearly, I am looking for how one would derive an expression for the capacitance of a system which consists of two conducting spheres of radius $a$ separated by a distance $d>2a$. I ...
2k views

### Can you charge a capacitor with only voltage (without current)? If No, then how does a capacitor correct power factor?

Let me explain you why I am asking this question. The other day I was studying about power factor correction of a (step up or any) transformer. It said that on the output side of transformer's ...
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### Charge accumulated on a hemispherical bulge on a conducting sphere

Consider a conducting sphere of radius $R$ which has a small hemispherical bulge on the surface of radius $r$. The sphere is given a charge $Q$. The expression for the charge accumulated on the ...
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### Pathways of Dielectric breakdown

I wanted to know if Dielectric breakdown can choose pathways different from its immediate electric field direction for example in the picture If Pathway 1 is of higher Dielectric Breakdown strength ...
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### How do you determine the electromotive force when the negative plate of the capacitor is connected to the positive terminal?

$\newcommand{\d}{\mathrm{d}}$We have a square wave source with period $T$ and voltage $V_0$ connected to a circuit which is has a resistor of resistance $R$ in series with an uncharged capacitor of ...
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### Why won't the bulb light? [closed]

Here's what the marking scheme says: "Capacitor gets charged first and acts as an insulator/blocks current". However, electrons flow from negative to positive, so shouldn't the electrons ...
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### How do capacitors restore their charge?

I understand the basics of how capacitors work, but I can’t seem to wrap my head around this. If there is a non-conducting material in between the two plates, and you place a capacitor into a DC ...
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### Trick question: why do dielectrics and isolated conductors affect capacitance differently?

This question confused me a bit, but I figured out the answer. I just want to share this trick question here. Trick question: Dielectric material produces net surface charge when placed in electric ...
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### Is it possible to connect thermal masses (capacitors) in series?

We can find the equivalent capacitance of two electrical capacitors if they are connected in series or parallel. And if two thermal masses are connected in parallel the method of finding the ...
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### How to measure voltage induced in coil due to an oscillating bar magnet using null method? [closed]

Here we're trying to measure the maximum emf induced in the coil using null method. I can understand what the book means by 'a kick'. I can't understand how this circuit works. For example, how is the ...
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### Charge on capacitors after connecting them

In Figure 1, how can we be sure that after the switch is closed, in each capacitor, the plates would carry an equal positive and negative charge? Why can't it be the case that say in the capacitor in ...
51 views

### Charge distribution on a system of 3 capacitors when the middle one is earthed

Three conducting sheets 1,2 and 3 are placed parallel to each other such that separation between them is negligible. Sheet 1 and sheet 3 are given charges $+Q$ and $+3Q$ respectively. $Q=3 \space mC$ ...
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### What will happen if we connect a capacitor with a dielectric?

Say we have a capacitor of two parallel plates, full of air in between, connected to a battery that allows it to charge up. Now we deposit a dielectric plate between both capacitor’s plates, while ...
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### What’s happening with ions while a capacitor is being charged by a battery?

An uncharged capacitor has an equal amount of positive and negative charges in both plates, meaning there are ions in both plates which altogether have a neutral charge. When you connect an uncharged ...
1 vote
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### What is the electric field between two plates with a hole each (the holes also parallel)?

Suppose you have two charged parallel plates, and an electron on the negative plate. It would move in the electric field to the positive plate. If, however, there was a hole on each of the plates, ...
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### Enhanced capacitance by magnetism?

Consider the first picture. This is much like a parallel plate capacitor charged by a battery. But instead of parallel plates we are using parallel rings. The rings are attracting each other because ...
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### Confusion regarding Capacitance of Vaccum

Capacitance is given by:- C = $\frac{Q}{V}$ $Q$ represents change in charge. $V$ represents change in potential difference. If the dielectric material of a capacitor is vacuum, charges will be able to ...
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### Capacitors in Series and Parallel/Dipole

I'm struggling a bit understanding capacitors. I understand all the basics/formulas of capacitors in series and in parallel, but is lacking a complete intuitive understanding of how capacitors. So I ...
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### Various shapes of insulator in electric field

Given the capacitor below with large plates and small gap and a metal slab in between and a voltage applied between two conductive plates, we can prove easily there is electric field in the air gaps. ...
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### Is my understanding of capacitance correct?

a capacitor can store charge. if there's a great distance between the plates, the voltage (even if the charge we add is small) is going to be huge, because of the huge potential energy (and the fact ...
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### What does capacitance physically mean?

so im reading a bunch of textbooks on static electricity(high school level). and the capacitance concept keeps bugging me. C=q/V right. lets say we have a conductor. we place excessive charge on it. ...
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### Impedance in AC circuit

why in series $LCR$ circuit impedance is calculated by vector method even though resistance is a scalar quantity. They should have been added algebraically but instead have been added vectorially
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### Electric field and conservation of energy [closed]

I have a question of conservation of energy. Let's say I have two charged plates, one positively charged and the other negatively charged. Both have a hole and an electric field exists between the two ...
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### Energy to assemble a capacitor [closed]

Consider a body $\Omega$, inside of which a dielectric is present. We have a conductor on $\partial \Omega$. I am trying to understand the computation of the energy required to assemble the entire ...
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### How can a conductor with high capacitance store more charge at less potential?

In my textbook a statement is given that goes like "for large C , V is small for a given Q". I am not getting it if charge on a capacitor is increasing ...
1 vote
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### How does a capacitor bottom plate get charged positive in DRAM?

So, I understand of the NMOS transistor work's here (at least I believe I do). Electrons are flowing towards the capacitor plate from the drain here. So, I don't get how the plate connected to the ...
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1 vote
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### Capacitance between P-type semiconductor block and metal plate

I have been trying to understand and simulate the capacitance between a P-type (doping= 10^15/cm^3) semiconductor block and a metal plate with air gap between them. I used Sentaurus TCAD software to ...
1 vote
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### Why do two infinite planes contribute to Electric Field but not two surfaces in co-axial cylinder

I understand why the electric field between two infinite planes is $\frac{\sigma}{\epsilon_0}{\vec{e_z}}$. Both planes contribute to the field - the upper positive charged plane "pushes" ...
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1 vote
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### Problem on capacitors [closed]

Consider a two plate capacitor, with a voltage across them equal to V, that is placed inside a metal box (it is the same as adding another metal plate on each side of a capacitor and connecting them ...
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1 vote
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### Charge in a capacitor circuit [closed]

Firstly switch K is being closed and that one capacitor is being fully charged. Then the switch K is being opened again. What will be the difference of total charge in the system before and after ...
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### Why is the product of the $L$ and $C$ matrices for coupled transmission lines diagonal?

Background - transmission line $\newcommand{\ket}{\left \lvert #1 \right \rangle}$ A transmission line can be modeled as an infinite sequence of inductors and capacitors: ...
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### Why does the charge redistribute among the metallic balls connected to current carrying wires?

In the above circuit,as soon as the switch is closed,current flows in the circuit,maintaining constant potential differences between each resitors(V/2) at steady state,causing constant potential ...
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### Deforming LC circuit into dipole antenna

I once learned in school, and as far as I know this is also a common thing in many introductory physics books, that a parallel LC circuit can be "bent open" into a dipole antenna, like this: ...
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### Signal Speed in Coaxial Cable

I want to calculate the signal propagation speed in a real life coaxial cable. I have the data sheet which tells me its impedance and capacitance per unit length. For long parallel wires carrying ...
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### How different material capacitors can develop different charges?

I learned in a video tutorial that same battery could produce different charges based upon different capacitance of the materials used. Also A capacitor fully charged has the same voltage as the ...
1 vote
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### Why is the lightning waveform modelled by double exponential waveform?

As per wiki: The electric current within a typical negative CG lightning discharge rises very quickly to its peak value in 1–10 microseconds, then decays more slowly over 50–200 microseconds. Why ...
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### Is my uncertainty when fitting a curve to data from an oscilloscope too small?

I was trying to measure the capacitance of a (large) capacitor using discharge decay. I saved the data from an oscilloscope while taking measurements, and it recorded about 250,000 points. I noticed ...
1 vote
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### Why does touching the microphone cable stop my headphone from humming?

This might sound like a techical problem, but i'm more interested in the physics aspect of it. I have headphones that are connected to my pc with a single cable. I also have a microphone attached to ...
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1 vote
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### How is the total energy conserved when an electron moves through a plate capacitor and gets accelerated?

We assume that the electron enters the plate capacitor with a constant velocity. If we also assume that the electric field is homogeneous and edge effects can be neglected, a force along the y-axis ...
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### What size capacitor do I need to power a 12v circuit requiring .002A for 1 second? [closed]

I am attempting to make a flashing 12v signal into a constant (ish) 12v signal by smoothing it out. When the flasher is in its "off" phase Im needing to simualate the same as when its on. (...
1 vote
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### Work-energy theorem giving no work done on capacitor and dielectric when dielectric removed from capacitor [closed]

For this problem, Do you please know why when considering that the capacitor and dielectric is our system, the work energy theorem gives the wrong sign for the change in electrostatic potential ...