Questions tagged [capacitance]

The ability of an object to store electric charge.

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Microscopically (Classically), How does Current keep Increasing with Decreasing Electrostatic Field inside of Capacitor in a $R(L)C$ circuit?

Assuming the capactior is intially charged with voltage $V$, then detached from the voltage source I know mathematically by using: $$C\frac{dV_c}{dt}+\frac{V}{R}=0$$ I can get an expression of the ...
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Can Electric field pass through the insulators? [closed]

I tried to build parallel plate type capacitor. In that capacitor I placed one semiconductor material as dielectric and I covered this semiconductor by insulators from a both side. Then I placed ...
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Derving circuit equations for $RLC$ circuit such that order does not matter [closed]

Can we derive the circuit equations for an $RLC$ circuit from first principles in a way that makes it clear that the order of circuit elements doesn't matter? Any help is greatly appreciated!
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Current through a capacitor in AC Circuits

I'm a little confused on the equation for the instantaneous current through a capacitor in AC circuits. My textbook has it as: $$i_C = \omega CV \ cos(\omega t + \pi/2) = -\omega CV \ sin(\omega t)$$ ...
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Why Is Capacitance Not Measured in Coulombs?

I understand that the simplest equation used to describe capacitance is $C = \frac{Q}{V}$. While I understand this doesn't provide a very intuitive explanation, and a more apt equation would be one ...
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Is AC current equation in an RC Circuit wrong? [duplicate]

This is about the RC circuit current equation in AC which is similar to and RL circuit and both these equation seem to have the same problem. The equation is I=(V0/Xc)sin(wt+90) where I is the ...
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Hole concentration distribution in MOSCAP

For a given p-type MOSCAP energy band diagram, I was asked to sketch the distribution of holes with respect to position. I understand why the hole concentration at the interface is $10^{10}/cm^3$ and ...
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3 answers
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Current sign convention RC and LC circuits

When deriving the equations for RC and LC circuits we substitute the current in the circuit with the time derivative of the charge on the capacitor. However, when I think about it, the rate at which ...
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1 answer
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What is the working mechanism for current increase with voltage increase (in case of a capacitor)

Image I have a loaded parallel-plate capacitor having capacity $C$ with a fixed charge $Q$ on the plates. It induces a voltage $U = Q / C$. If I connect a load with resistence $R$, then a current $I =...
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What happens if a charged capacitor is connected to the ground on both sides through resistors? [closed]

Imagine we have the circuit below: When the switch is connected to (a), we will be charging the capacitor. After the capacitor is fully charged, the left side of capacitor will be at 5V and right ...
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1 vote
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What is the current going into a resistor-capacitor parallel circuit and the current coming out of it? [closed]

I'm looking at the circuit below and know that I1 = I2. Can someone explain why those 2 currents are the same?
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How to derive the equation for capacitive reactance? [closed]

How to derive the equation for capacitive reactance $X_C$? $$X_{C}=1/(2\pi fC)$$ with $f=$ frequency, and $C=$ capacitance.
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How to derive the formula for total impedance, $Z$, in an $RLC$ circuit? [closed]

Where this is an AC circuit, how can we derive the below formula for impedance, $Z$? $R = $ resistance, $X_{L} = $ inductive reactance, and $X_{c} = $ capacitive reactance.
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Energy in $RC$ Circuit

In circuit A, the total energy dissipated in the resistor is $\frac{Q_i^2}{2C}$ which equals the initial energy, meaning that all the energy was dissipated in the resistor, and lost as heat. Here's my ...
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Is electrical capacitance different at relativistic velocity?

A 2 parallel plate capacitor has a capacitance proportional to the area of the plates and inversely proportional the distance between the plates. If the plates are perpendicular to the direction of ...
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I have a doubt regarding energy stored in capacitor [duplicate]

I came across this question while practicing some problems regarding capacitor. Here's the question.. . A capacitor has an energy of U. This capacitor is then connected parallel to another capacitor ...
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1 answer
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If i consider capacitor discharging process..and i take wires resistance zero..put the capacitor in vacuum .. where does all the energy go...? [duplicate]

If i consider capacitor discharging process.and i take wires resistance zero.put the capacitor in vacuum . where does all the energy go?like is it the displacement current .but there's no medium then....
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1 answer
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Potential of a capacitor

I'm learning about capacitors, and i cannot visualise what potential difference of the capacitor is. I do know that potential of a charge is work per unit charge which is (kq)/r , where q is the ...
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How is the work done by a battery (when connected to a capacitor) independent of time?

We know that W bybattery = V(It) = VQ, which is time-dependent. But when the battery is connected to a capacitor then W bybattery = 1/2 (CV^2), where C and V both are time-independent, hence W ...
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1 answer
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Why is the net charge between two adjacent plates of capacitors in series considered neutral? [closed]

The right-most plate of C1 connected to the left-most plate of C2 is said to be isolated from the circuit. How is the left-most plate considered positive and the right-most plate negative?
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Why does changing the permittivity of the dielectric within a capacitor not have any effect on the electric field opposite the plate?

Utilizing FEMM 4.2, I built a pair of simple parallel plate capacitors, however I oriented them so that the anodes of these capacitors faced each other. As expected, the electric fields of the two ...
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2 answers
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Discharging capacitor: Series vs Parallel

Pretty basic stuff, but to be honest I haven't found a circuit diagram showing a capacitor discharging in parallel. The only scheme I can come up with is shown here: $\color{gray}{\textbf{[ Edited ]}}$...
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Electrostatic energy of capacitors and point charges

A number of questions have previously been asked about electrostatic energy for a system of conductors. But I am still confused about this topic. Suppose we have an ideal capacitor consisting of two ...
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1 answer
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Anti-gravity effect from charged capacitor? (correction)

A Reddit user called GratefulForGodGift has hypothesized that an electric field could warp spacetime. Consider the electrostatic field energy $\epsilon$ stored in a parallel plate capacitor given by: $...
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Questions about Maxwell capacitance matrix and reference point selection

Let's consider a system of n conductors. If I'm not mistaken, the Maxwell capacitance matrix tells us that the following system of equations applies: \begin{align} Q_1 &= C_{11}V_1 + C_{12}V_{12}...
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Electric current through the resistor of an AC $(L)RC$-circuit

I have a question regarding more complex circuits. For the sake of simplicity, suppose we have an AC source with an alternating voltage $U=U_0\cos{(\omega t)}$ and the angular frequency $\omega$ tied ...
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1 answer
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Dependency on capacitance [closed]

We know that when capacitance of a capacitor changes,it means the distance between the plates changes and as potential difference of the capacitor is dependent on the capacitor, i.e ($V=Ed$), the ...
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Connecting only one plate of the capacitor to the positive terminal of a battery [duplicate]

Suppose that the positive terminal of a battery is connected to one of the plates of the capacitor, and the other plate isn't connected anywhere. The other terminal of the battery is connected to a ...
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Residual charge in capacitors with inhomogeneous layered dielectrics

In a capacitor with two layers of different leaky solid dielectric materials sandwiched between the plates with different dielectric constants, free charge will accumulate at the dielectric interface ...
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Why don't the ends a switch function as a capacitor?

I was recently reading about one capacitor being used to charge up another capacitor. In this example, a capacitor is charged by a battery, and then the battery is removed. The charged capacitor is ...
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AC voltage and DC polarization vector

The device is infinite in X and Y axis. there is an alternating voltage source on top of the device with angualr frequency $\omega$. and the polarization vector is given by $P_0 \hat z$ which P_0 is a ...
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Eqv Capacitance of a Spherical Shell half filled with a Dielectric Medium [closed]

Given below is the diagram of a Spherical Shell filled with a Dielectric Medium in right half of the Shell. Find the Equivalent Capacitance of the given Shell. Attempt: We know that the Equivalent ...
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Unable to derive Grand Canonical Free energy for single electron transistor (SET)

I am try to derive the expression for Grand canonical free energy for single electron transistor (SET) and started with a simpler case as shown below from Physics of Nanoelectronics by Tero Heikkila: ...
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Why the charge in each capacitors plate are equal in magnitude in series combination?

Suppose two capacitors are connected in series, I understand that external plates gets equal magnitude because of the batteries terminals, but how does the internal plates also get the charge with ...
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1 answer
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How to model a circuit with resonant inductive coupling?

I need to model (write the equations for) a circuit with resonant inductive coupling, such as the one in the picture below. The picture is taken from the Wikipedia article on Resonant inductive ...
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Behavior of the current in a purely capacitive circuit during the two quarters of a half cycle

For a purely capacitive circuit driven by an AC source, $v(t)=V_0\sin\omega t$, the current through the circuit is given by $i(t)=I_0\cos\omega t=I_0\sin(\omega t+ \pi/2)$. A. For the first quarter of ...
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What is the correct derivation of energy stored in parallel plates capacitor?

I am little confuse in deriving the energy stored in the capacitor. I read two different derivation in totally different way but yet getting the same value. Here they have calculated work done by ...
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What is the meaning of potential of the capacitor?

I am little confuse about the potential of the capacitor. Suppose we have two parallel plates of capacitor and both have equal and opposite charges on it. Let say plate "A" has positive ...
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1 answer
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Infinite conducting plane [closed]

Let $\pi$ be an infinite conducting plane laying in $z=0$. the plane is kept in potential of 8 volts, ($\phi(z=0)=8[V]$). Prove or disprove: the surface charge density - $\sigma$ is well defined.(...
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How is energy "stored in an electric field"?

My physics teacher told me the statement "The energy of a capacitor is stored in its electric field". Now this confuses me a bit. I understand the energy of a capacitor as a result of the ...
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How much can we push the plates of capacitor?

I am currently a highschooler and came across this question in physics A capacitor of plate area $A$ and separation $d$ is connected to battery of emf $V$ and is charged to steady state. Now the ...
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Electric Power of Displacement Current

Say we have displacement current $I_d$ inside a plate capacitor of alternating voltage $V(t)$. We use the formula for electric power on the displacement current: $P=I_dV$ What does $P$ account for? ...
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Impedance Calculations for Parasitic Resistance, Capacitance, and Inductance

I have recently taken a look at basic electrical engineering topics, and I am having difficulty calculating impedance for parasitic elements. I am trying to find the impedance formulations for real-...
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Cant understand why $C_1$ and $C_1$ are in parallel?

We need to find the equivalent capacitance in this question. As in the solution on this website: https://www.toppr.com/ask/question/take-c140mu-f-and-c260mu-f-in-the-figure-calculate-the-equivalent-...
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1 answer
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How does a capacitor discharge through another capacitor and resistor?

So if a charged capacitor (say unit PD and charge), discharges across a resistor (say unit resistance) in series with an identical (uncharged) capacitor, how would I deduce the resultant pd? Because ...
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Relation of potential difference and charge in a capacitor

So, there is something regarding capacitors which is bothering me. It is said that in capacitors connected in parallel, the charge is divided between different capacitors, while potential difference ...
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How can the charge on a plate of a parallel plate capacitor (even if grounded) ever be zero, given that the other plate will create a field

I recently came across this answer https://physics.stackexchange.com/questions/193258/grounding-a-capacitor#:~:text=As%20a%20rule%20of%20thumb,though%20it's%20voltage%20is%20zero. while studying ...
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Is there a way to mathematically model the coupling of Quantized EM fields in macroscopic circuits?

I want to investigate (if it hasn't been done yet, which is very unlikely) how the coupling of a quantized em field couples to a circuit through for example an inductor. How can one do this? The ...
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What could be the cause of a limit in the voltage supplied to a capacitor?

Recently I built a very basic 2-stage coil gun for a school project. Each coil was powered by an electrolytic capacitor. In order to charge the capacitor, the coil connected to an IGBT (insulated-gate ...
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Why electrostatic energy of a capacitor is not taken as negative?

When we derive the equation for potential energy between two nearby point charges the final result says if both charges are of similar polarity then only we take potential energy of the system as ...
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