Questions tagged [capacitance]

The ability of an object to store electric charge.

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2 answers
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Net bound surface charge density of capacitor

Q. In a parallel plate capacitor, two dielectric slabs of thickness 5 cm each are inserted between the plates and a potential of 100 V is applied across it. The value of the net bound surface charge ...
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How to determine current as a function of time in an RLC circuit with variative capacitor?

I was given this problem: The image shows an RLC circuit which consist of a constant voltage source $\varepsilon$, an inductor with inductance of $L$, a resistor with resistance of $R$, and a ...
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1 answer
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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 (...
1 vote
1 answer
196 views

Why is the field inside a capacitor not the sum of the field produced by each plate?

In this answer by David Z, we can read, When discussing an ideal parallel-plate capacitor, $\sigma$ usually denotes the area charge density of the plate as a whole - that is, the total charge on the ...
1 vote
2 answers
103 views

How can this circuit be simplified in the first moments after the circuit breaker closes?

The book states that in this circuit after the transient the branch with the capacitor can be ignored while the branch with the inductance can be considered constituted only by a resistance. This ...
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0 answers
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An RLC series circuit with current equal to one half the resonant current [closed]

Consider a RLC circuit coupled in series supplied by the AC voltage v= 30 sin(w t), R=50 W, L= 600 mH, frequency f=5 kH. The inductor is a solenoid and the capacitor has cylindric configuration. The ...
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1 answer
25 views

Does the current inside a capacitor with dielectric becomes zero, if a DC (constant)voltage is applied?

Imagine a capacitor with dielectric with conductivity $\sigma$ and constant voltage source with voltage applied say $V$ is applied to it's ends, now using Ohm's Law we have $ \vec{J} = \sigma \vec{E}$....
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Charges on conducting shell with a conducting sphere inside it

If I have a spherical capacitor which is composed of a conducting sphere surrounded by a conducting shell and the space between them is filled with a dielectric , I assumed that the charge on the ...
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1 answer
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-...
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What is $Q$ in the energy stored in a parallel plate capacitor?

If we have a parallel plate capacitor like the one below the energy stored in it can be give by $$ U=\frac{Q^2}{2C}$$ $\bullet$ C is the capacitance of the capacitor Now is the $Q$ the free charge on ...
4 votes
2 answers
688 views

What is capacitance, in general?

In circuit analysis software capacitance can be measured between any two nodes of a circuit or of a multiterminal device. In practical terms we take $C_{ij}$, the capacitance between $i$ and $j$ as ...
1 vote
2 answers
87 views

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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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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1 answer
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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 ...
2 votes
2 answers
668 views

How Are Electromagnetic Waves Produced?

How EM waves are produced say by a capacitor of an LC circuit here if $E$ is increasing in upward direction? My thoughts Thought 1:- If E is increasing E flux is increasing thus B field must be ...
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3 answers
228 views

Maximum charge of a capacitor

Suppose we have a capacitor charged with charge $Q1$ Then an electron beam hits the positive plate of the capacitor, thus increasing the charge of the capacitor (the battery will begin to deposit the ...
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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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1 answer
41 views

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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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 ...
1 vote
2 answers
937 views

Charged dielectric/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 votes
1 answer
47 views

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 ...
1 vote
2 answers
3k views

Redistribution of charges when capacitors are connected in series

This question is asked before but I didn't get the answers It is known that when 2 unequally charged capacitors are connected in parallel then the charges redistribute themselves till the voltage ...
-1 votes
2 answers
50 views

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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0 answers
41 views

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 ...
-1 votes
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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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1 answer
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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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1 answer
162 views

Why doesnt a capacitor discharge when you ground one end?

I have grounded one end of my capacitor after charging it but the voltage drops at a steady pace not as if it has lost charge. Is this because the opposing charges on the opposite plate are keeping ...
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3 answers
275 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}_{...
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2 answers
104 views

What's the electric field inside a capacitor with AC current?

In DC-circuits the Electric field can be easily calculated under the conditions the field is homogeneous: $U = \int E \,\mathrm{ds} = E\,d$. Now I wonder what if you apply an alternating Voltage $U(t)...
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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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1 answer
2k views

What happens to the energy of a capacitor after a dielectric is inserted?

Consider a parallel plate capacitor having capacitance $ C$ and charge $Q$. then the energy of the capacitor will be $\frac{Q^2}{2C}$. Now if a dielectric is inserted, then $C $ increases and thus the ...
1 vote
1 answer
494 views

Earthing a system of parallel plates

our sir has taught us that when in a system of conducting infinite plates kept parallel to each other, when any one of them is earthed, then the charges present on the free ends(i.e. the open sides of ...
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1 answer
929 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 ...
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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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1 answer
49 views

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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2 answers
250 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 ...
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1 answer
60 views

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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1 answer
162 views

Product of Capacitance and inductance in parallel plates

I was solving this problem: I was asked to find the capacitance per unit length, which I did (in cgs units) $$C=\frac{w}{4\pi h}$$ and to find the inductance per unit length $$L=\frac{4\pi h}{c^{2}...
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1 answer
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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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0 answers
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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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2 answers
68 views

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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2 answers
62 views

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 ?
2 votes
3 answers
230 views

Does insulating sphere have a capacitance?

A conducting sphere with radius $r$ has capacitance $C=4\pi \epsilon_0 r$. This can be derived as follows: $$ C=\frac{Q}{V}=\frac{Q}{\frac{Q}{4\pi \epsilon_0 r}}. $$ Now I am wondering if this ...
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1 answer
177 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 $t=18$ ...
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1 answer
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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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