Questions tagged [capacitance]

The ability of an object to store electric charge.

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What is the capacitance of ferrodoxin molecule?

On Wikipedia it says that a ferrodoxin molecule is a biological capacitor which transfers electron to change the oxidation state of iron from $\text{Fe(II)}$ to $\text{Fe(III)}$. Now I simply want to ...
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Work done by battery [closed]

In charging a capacitor to a charge $Q$ Is there an equivalent to this in setting up current through an inductive circuit? Energy stored in inductor $= 1/2Li^2$ What would be the work done in setting ...
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Charging of capacitors [closed]

A capacitor with capacity C=10 µF is charged from a battery with ℰ=4.5 V and r=50 mOhm through a semiconductor diode VD whose idealised voltage-voltage characteristic is shown in the figure. U, В is ...
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Why bridge rectifier circuit is widely used to make power supply? [migrated]

Why bridge rectifier circuit is widely used to make power supply?. which is better, bridge rectifier with capacitor or without capacitor?
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DC Bias Characteristic of Ceramic Capacitors under Transient

It's pretty well documented that many ceramic capacitors will "shed" capacitance with increasing DC bias. Seems that the mechanism is pretty well outlined too. (The physics behind DC voltage ...
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Discharging two capacitors in series

I have two capacitors, C1 and C2 charged in series and I want to discharge them through a resistor. Does the discharge equation still hold here for each of the capacitor? For C1, $$Q_{1}=Qe^{\frac{-t}{...
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Energy stored in capacitor over time

I know that the maximum energy that can be stored in a capacitor is: $$ U = \frac{Q^2}{2\,C}\,. $$ What I am asked is to say how much energy was stored when half of the electric charge that could be ...
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LC circuit in spring system

We have a setup of a metal spring with a mass. This would oscillate nicely. Additionally, an inductor with a capacitor also oscillates nicely. If we were to combine these two setups, where the mass is ...
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Is this formula for a hollow sphere or a solid sphere?

In the above image, my book has given a formula for calculating the electric potential of a sphere: $$\fbox{$V=\frac{Q}{C}$}\tag{1}$$ Here, $C=\frac{r}{k}$. Is $(1)$ a formula for a hollow sphere or a ...
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What will hold more charge in a capacitor? Activated carbon at 500 m^2 per gram or Copper powder at 2.7 m^2 per gram? [duplicate]

Activated carbon is less conductive then copper. With these ratios would copper hold more charge or would activated carbon. Online you can find the conductivity and resistance of copper. but I am ...
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Relation between conductance and capacitance?

Say I have a material like activated carbon VS copper. Activated carbon has a surface area of 500 meters^2 per gram. Copper is a lot more conductive and with copper powder at .3-.5 microns I’ve seen ...
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Why is it not possible to calculate the distance of a sensing electrode to a grounded object based on the measured capacitance?

Hello I am currently working on a scientific fair project where I want to measure the capacity between a sensor plate and a moving grounded object and thus calculate the distance between them. So far ...
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If my capacitor plates have a high surface area due to porosity such as sintered metal. Can my capacitor plates be as thick as I want and hold charge?

Say I have a capacitor plate. But this plate is made from sintered metal so it has a really high porosity and surface area. Does this mean I can increase plate thickness to any size I want due to the ...
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Electric flux in inductor

An AC circuit is set as follows The circuit consists of a voltage source, an ideal inductor with inductance $L$ and a ideal capacitor with capacitance $C$. The current through the circuit is $i(t)= ...
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Is the commonly derived Gauss' law for a parallel plate (insulator/conductor) often derived wrong? [duplicate]

I am very confused about plates (conductors/insulators) and applying Gauss law. It seems like gauss law for the isolator is very often derived wrongly. In short: if you have an infinite plate (...
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What is electric permitivitty?

I have read 10 different explanations for this in 10 minutes. By definition, to permit means to allow something, but some sites say that it is actually how much a material resists the electric field? ...
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Electrical Power and stored power

The simple circuit below, consists of a battery with constant electromotive force (efm), $\epsilon_0$, a capacitor which capacity varies with time $C(t)$ and ,to make it simple, ideal wires (zero ...
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When two capacitors are connected in parallel, do they drain battery quicker?

My question is actually my answer to a question I asked myself i.e 'how does potential difference remain same for both capacitors which are connected in parallel, and not get distributed' When 2 ...
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Can you increase capacitance of capacitor by sandwiching a high dielectric constant material between two strong insulators?

My very limited research into dielectric materials has suggested that the higher the dielectric constant of a material, the less insulating it is. So why not just have some material with extremely ...
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Disagreement in the magnetic field inside a capacitor depending on the Maxwell equation

Consider a capacitor of two parallel circular plates of radius $a$ separated by an air gap of width $d$, where $d \ll a$. The capacitor is connected an alternating voltage source, $ V = V(t)$. To find ...
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Does the Casimir force also define a 'casimir capacitance?'

If you have two plates with distance $\Delta d$ then a Casimir-force will exist between the plates. In contrast if you have two other capacitors with charge $+Q$ and $-Q$ there will be also a force (...
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What does equivalent capacitance in general mean?

If you have some capacitors in series then their EC (= equivalent capacitance) means the capacitance of the capacitor which will store the same charge as any individual capacitor in the series when ...
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Power equation in railgun operation?

In a capacitor discharge through a plain resistor, the capacitor power supplied at any instant is VI; the power dissipated in the resistor is I²R. So VI = I²R. Consider a railgun operated with a ...
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Potential energy of parallel plate capacitor

I am trying to calculate the electrostrictive strain S on a parallel plate capacitor. For that, I use Young's modulus Y and the formula $$S = \frac{F}{AY}$$ Since the area A and the Young's modulus ...
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Heat dissipated in a capacitor network on switching a key

Suppose we have this capacitor network connected to a battery($V$) with the switch initially open. On closing the switch whilst keeping the battery connected, we find that some heat is dissipated. We ...
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Capacitors and electrical energy [duplicate]

We know that the potential energy stored ina capacitor connected to battery of emf V is: (1/2)QV . But the work done by battery in the process is QV where does the half goes ?
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Capacitor electromagnetic radiation

The plate capacitor is charged and discharged with sinusoidally changing electric current. Why does a capacitor emit electromagnetic radiation?
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Why the charge is the same for capacitors connected in series?

For example in this figure, I can understand that the charge on plates 1 and 4, and plate 2 and 3 must have the same value because of charge conservation. Is there any justification that plate 2 must ...
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Quality factor of LCR circuit

If we are given a parallel or series LCR circuit, we know the quality factor of these circuits ( which we can see in many books). But if we are given a LCR circuit with the three components connected ...
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Is there a magnetic field around a fully charged capacitor?

I know that a magnetic field exists when a capacitor is in the process of charging/discharging: (a) But what if the capacitor is fully charged? Will the magnetic field still persist? Something like: ...
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How do I Calculate capacitance?

There was another question about calculating capacitance between arbitrary shaped conductors where the accepted answer was effectively: "Create a grid, place the shapes on the grid giving each ...
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Problem understanding the use of differentials in equation for energy stored in a capacitor

I was going through the Feynman Lecures on Physics Vol. II and arrived at section 8.1, where the equation for the energy stored in a capacitor is obtained. We consider now the energy required to ...
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Finding potential difference for one side of a parallel plate capacitor with dielectrics in parallel [duplicate]

I'm doing some homework problems and there's a question that asks for the potential difference of the left side of a parallel plate capacitor that looks like this: ...
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About parallel plate conductors' capacitance

Capacitance of the parallel plate conductors is $εA/d$ where $A$ is the area of each plate and $d$ is the distance between them. My question is, instead of 2 identical plates, what if we used 2 ...
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Energy of capacitors in Series and Parallel

I'm just confused in general about what happens with charge, voltage, etc in parallel and series circuits with capacitors. Anyways, I'm trying to find the total energy stored in $2$ equivalent ...
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Capacitors filled with parallel $n$ dielectrics

I'll be brief. In cases where we have a capacitor filled with an $n$-amount of different dielectrics, each and everyone one right next to the other, is it okay to re-think the problem as having n ...
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Electric Potential along $x$-axis because of 2 charged parallel planes

I'll get to the point. I know how to find the expression for the electric field inside two charged parallel planes, and I understand how I can then use that information to find the electric potential ...
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Capacitance of a dielectric capacitor with two sphere electrodes instead of parallel plates

EDIT: title changed to be more descriptive. I would like to calculate the capacitance of a material (in plate form with thickness d and a known permittivity $\varepsilon_r$ ) between two sphere ...
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Fully charged capacitor is connected to another battery

Suppose an empty capacitor with a capacitance A Farad is connected to a B voltage battery. After the capacitor is fully charged, ...
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Time constant versus half-life — when to use which?

In some systems we use half-life (like in radioactivity) which gives us time until a quantity changes by 50% — while in other instances (like in RC circuits) we use time constants. In both cases the ...
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Can anyone please tell me what will be the final charge distribution? [closed]

What happens after we close the switch, (a) $c_1=$ capacitance of the upper parallel plate capacitor having $Q_1$ charge (b) $c_2 =$ capcitance of the lowerparallel plate capacitor having $Q_2$ charge ...
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Particle Coupling in Ion Trap

Ion traps are very complex, but one of my Physics Olympiad textbooks presents a simplified model of a resonating charged particle in an ion trap A tuned circuit consists of an inductor and a parallel ...
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Can anyone please tell me the location of energy?

the formula $Q^2/2C$ gives the energy for a concentric spherical capacitor, where $C=$capacitance of the capacitor and $Q=$charge but i cannot understand where the energy is situated. is it in the ...
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Capacitance of current carrying conductors

I'm studying transmission lines, and we often model them using Resistors, Inductors, and shunt capacitors. Since a current carrying wire has an associated magnetic field, it makes sense to calculate ...
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Calculating the Capacitance for Spheres

On my homework, I came across a question that asks to compare the capacitances of these two spheres. And answer is $1/2$. I know the formula is 4πε0R for a sphere, but the answer to why it is linear ...
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Capacitance of a dielectric passing through a capacitor at speed $v$

I'm having trouble understanding the result of the total capacitance when a dielectric of of area $A$ (of sides $l \times l$) is passing through a capacitor with plates of area $2A$ ($2l \times l$) ...
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Why is the relation between voltage ratio and frequency a linear one in a lumped transition line?

In an experiment the cutoff frequency of a lumped transmission line is determined by measursing the ratio of the output/input voltages. The lumped transmission line is a ladder network of 40 ...
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Resistance-capacitance (RC) circuit

My textbook says: "This continues until the voltage across the capacitor matches the emf of the battery" If I were to have a resistor in series with a capacitor, would the voltage across the ...
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Question about the impedance of a RLC circuit

I made an experiment with a RLC circuit, and I found the resistance, the capacitance, and the inductance with measures. So I decided to calculate the impedance of the circuit, depending on the ...
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Common potential of two capacitors in series

I have read in a book that if two capacitors are connected in series then their common potential will become $$\frac{C_1 V_1-C_2 V_2}{C_1+C_2}$$ I just need to know how this happens. Any help will be ...
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