Questions tagged [capacitance]

The ability of an object to store electric charge.

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1answer
33 views

Why does a floating capacitor act differently than a grounded capacitor?

I'm having difficulty understanding why a floating capacitor will store less charge than a grounded capacitor. Imagine you have two parallel plates and a low DC voltage source like 5V, with the ...
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32 views

How does RF communication between electronic circuit elements affect the circuit?

The other day, a friend and I were looking at a simple resistor-capacitor-inductor circuit. As we were looking at the circuit, he mentioned that the capacitors and inductors "talked" to each ...
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1answer
40 views

Spherical Capacitor [closed]

How would we derive the equation for the capacitance of a spherical capacitor when the inner sphere has been earthed? I am aware of the formula $\frac{4\pi \epsilon_0}{\frac{1}{R_1}-\frac{1}{R_2}}$ (...
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1answer
25 views

Why is capacitance a constant (isolated charged sphere)

I'm not getting why is the capacitance a constant, and how you can deduce it from the potential and charge. The potential of the sphere is (in the radial magnitude) $V(r) = \dfrac{kQ}{r} $ if $r >...
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General Expression for capacitance of any type [closed]

The capacitance of a parallel plate capacitor is given by C=Aε/d. For concentric spherical capacitor the value of capacitance is given by 4πεba/(b-a) (where b is the radius of the outer sphere and a ...
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2answers
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What will happen if a capacitor is given a very large amount of charge within a very small period of time? [closed]

When a capacitor reaches its maximum potential, and charge is still being given to it, it just leaks through. A teacher asked us to consider it similar to trying to pour a jug of water into a ...
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4answers
48 views

Differential Equations in a Discharging RC Circuit in Parallel

Please consider the following RC circuit as context: Assume that the circuit has been connected for a long time. If switch S has been opened at $t=0,$ the differential equation used to solve for the ...
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1answer
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RLC - CLR - RCL Transfer function

I have problem because I don’t understand the difference between CLR RLC and LCR, they are the same no ? They have the same composant just placed in different ways, I did already found the Transfer ...
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Homework problem: Based on charge distribution on parallel plates [closed]

My attempt: Applying conservation of charge and gauss law I am getting a nonsensical result that $q_2-q_1=-Q$ and $3Q$ both. I have considered Gaussian surfaces between three sets of consecutive ...
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What is the possible arrangement that requires the minimum number of capacitors? [closed]

My textbook says the following: An electrical technician requires a capacitance of 2uF in a circuit across a potential difference of 1kV. A large number of 1uF capacitors are available to him each of ...
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How to solve questions having two different dielectric with two different dielectric constants such as the one below? [closed]

The space between the plates of a parallel plate capacitor is completely filled in two ways. In the first case, it is filled with a slab of dielectric constant $K$. In the second case, it is filled ...
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6answers
366 views

How do capacitor plates maintain equal but opposite charges in a circuit?

I have a question regarding capacitors and their charge neutrality. When capacitors are used in circuits, the assumption is often made that the plates of the capacitors have equal and opposite charges....
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2answers
50 views

LC circuit with dissipation [closed]

I know that the differential equation that describes this kind of circuit is $$\frac{d^2 q(t)}{dt^2} = -\omega^2 q(t) \, .$$ I was wondering how to model the case where we have dissipation of energy. ...
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2answers
41 views

Understanding the ordinate at $R=0$ in a capacitor experiment [closed]

I've done an experiment to study a capacitor's discharge time and calculate an unknown capacitor's capacitance. With the help of an oscilloscope, I measured the time it took for the capacitor's ...
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2answers
42 views

A circuit with three capacitors in series

Here is a picture of the given circuit. Initially the switch is connected to the left side, and the question is what are the charge and potential difference across each capacitor ( capacitance is in $\...
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2answers
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Heat dissipated on switching the wire?

$C$ and $C_0$ are the capacitance of the capacitors. The wire marked with an arrowhead is to be switched from point 1 to 2. Resistance of wires is very very less (~0). Leaking of charge does not occur....
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1answer
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What is the charge stored by the capacitor?

I learnt that for an uncharged capacitor of capacitance $C$ connected with battery voltage $V$, the energy stored by capacitor is equal to $\frac{1}{2}CV^2$. But in this example for the capacitor ...
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1answer
26 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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3answers
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Is it necessary that a capacitor stores energy but not charge?

Is it necessary that a capacitor stores charge? The definition of capacitor given in books is that it store electric energy. So is it possible that the capacitor does not store charge but stores ...
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1answer
33 views

Is it necessary that a capacitor stores charge?

Is it necessary that a capacitor storage charge? I am a little bit confused. For example: if I take two concentric conducting shells and a positive point charge at the centre. Both the surfaces (outer ...
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1answer
71 views

Force on dielectric slab

My Doubt is regarding the procedure of calculating force on dielectric while it is being inserted between the capacitor plates (with or without battery). This is the theory behind it. Consider a ...
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2answers
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Capacitor between two equipotential surfaces [closed]

Is a capacitor possible between two equipotential surfaces? I asked my teacher and the explanation given was: There is an electric field between the two equipotential surfaces, thus energy is stored ...
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0answers
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Problem related to CR circuit [duplicate]

We know, that in CR circuit during charging of the capacitor, "growth of charge in the capacitor" occurs. But, we also know, that as the capacitor gets fully charged, current in the circuit stops ...
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1answer
26 views

Can one capacitor charge another connected by a single lead only?

My instructor presented the following problem on capacitors: Plates 1, 2, 3, and ...
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2answers
37 views

Is the overall energy conserved in this situation?

Imagine a fully charged capacitor. This will create an electric field, and if a fixed charged particle is nearby, it will possess some amount of electric potential energy. But what happens to the ...
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1answer
37 views

For which reason do we say that the charge surface density is rougly constant (uniform distribution) on a capacitor's plates?

Consider for instance a parallel plate, a spherical or a cylindrical capacitor. Usually we analyze it by considering the surface charge density on each plate uniform, i.e. constant along the plate. ...
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Crossover filter gives weird results

I was analyzing results of an experiment on a crossover filter and I was trying to take into consideration the parasitic resistance of the inductor L (called $R_L$). I know the theoretical crossover ...
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1answer
42 views

What happens with the electric field between two capacitor?

consider the schematic, we have two capacitors, $C_1$ is charged and $C_2$ uncharged. (connect the plates together to keep the plates neutrally charged). In principle $C_1$ generates an electric ...
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29 views

Conducting concentric spheres with charge Q connected by a wire with a switch. What is the potential energy before and after the switch is flipped? [duplicate]

A system of two conducting concentric spheres both having a charge of Q and the two spheres are attach with a wire that has an open switch, and the inner sphere radius is ¾ the radius of the outer ...
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Can a capacitor have zero potential when connected with another capacitor

I saw a question where it says that two capacitors of different capacitance $C_1$ and $C_2$. $C_1$ is charged with potential of $200\mathrm{V}$ and $C_2$ is charged with potential of $120\mathrm{V}$. ...
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1answer
33 views

Distribution of charges: parallel plates and potential [closed]

How do you calculate the charge distribution on three parallel plates which have unequal charges on them and then they are connected by a wire? Also, we need to calculate the field and potential ...
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0answers
11 views

Calculating energy exerted on individual atoms/molecules in a dielectric

If you have a dielectric material with a given dielectric constant (say one in a parallel plate capacitor for simplicity) that is polarized by a given electric field, can you calculate the effective ...
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Equivalent lumped element model of an inhomogenous distributed transmission line

Good day, I'm interested in an equivalent-circuit type problem that might be closely related to this question and its answer. What I am considering is sketched below: Essentially what I meant to ...
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2answers
178 views

Does the capacitance of a capacitor depend on the type of dielectric that is NOT between the capacitor?

In the image above there are two infinite planes. The infinite plane at $z = a$ has a surface charge $\sigma$ while the infinite plane at $z = 0$ has a surface charge $-\sigma$. The dielectric that ...
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1answer
26 views

$C$ circuit and electrostatic energy

My first question is either if there are capacitors in series/parallel or what does P mean in between them. The second would be the amount of charges in them, once the difference in electrical ...
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0answers
51 views

Time needed to charge capacitor [closed]

In the given circuit, the capacitor of capacitance $C$ is charged by closing key $K$ at $t = 0$. Find the time required to charge the capacitor upto maximum charge for the given circuit, if it were to ...
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1answer
74 views

What if I insert more charge into a charged capacitor?

Suppose we have a charged capacitor with charge = $Q_1$ and then an electron beam inside the positive plate of the capacitor. The electrons entering the positive plate are repelled by the negative ...
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Dielectric material and capacitor

First, If something is unclear because of my English, let me know. Assume I have a two-board capacitor connected to a power supply which delievers constant voltage value,and I am willing to fill it ...
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Why does single electron Coulomb blockade charging use $Q^2/2C$?

Classically stored energy of a capacitor is $\frac{Q^2}{2C}$. However, the difference in energy when a single electron travels across the gates should be $qV$ But in couloumb blockade calculations, ...
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71 views

Where does the energy go when I short a capacitor? [duplicate]

Please, help me find the mistake in this line of thought, or solve the inevitable question at the end. 🙂 suppose there are two facing plates with different charge $Q_1$ and $Q_2$ these two plates ...
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1answer
31 views

If a capacitor plate is equipotential then how come it has different potentials on the inner and outer plate during the charging phase?

I have a very fundamental doubt: Consider a capacitor with plates name $X$ and $Y$, Since the plates of capacitor happen to be conductors, they are going to have equal potential at all points. Now ...
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1answer
27 views

Solving RC circuit ODE without integral [closed]

while studying RC circuit, every college book solved voltage in a RC circuit in the same way of solving this ODE. $$ε= {\frac{q}{c}} + R{\frac{dq}{dt}}$$ $$q=VC(1-e^{-\frac{t}{RC}})$$ However I ...
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1answer
44 views

How to calculate the magnetic field for a capacitor?

I found this answer: Magnetic field in a capacitor But I don't understand some aspects. He says that due to the symmetry we can assume that the magnetic field has the form: $$ \vec{B}=B_\phi(r) \vec{...
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Point charge between two Concentric Conducting Shells in a RC Circuit

Suppose we have placed a point charge Q at distance, 'd' between two concentric, neutral conducting shells of radii 'a' and 'b'. We can connect the two shells through a resistor and switch. I wanted ...
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1answer
29 views

Parallel plate capacitor problem [closed]

I am trying to solve a numerical problem related to parallel plate capacitor. Given below is the problem: $The\;plates\;of\;a\;parallel\;plate\;capacitor\;are\;2\;cm\;apart.\;A\;slab\;of\;dielectric\;...
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1answer
23 views

Current in RC circuit using Thevenin's equivalents or Kirchoff's laws

Say we have a DC circuit with multiple capacitors and resistors (and batteries) in it. All capacitors are assumed to be initially uncharged. Suppose we're interested in finding the current through ...
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1answer
18 views

Adjustment Required for Force between Plates of a Parallel Plate Capacitor

The parallel plate Capacitor is not an Infinite sized charged sheet system. But in Most derivations of Force between the Charged plates due to the electric field and charges between/on the plates is ...
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Self-capacitance of electrodes in capacitors

I thought about a way in which we could increase self-capacitance of electrodes in a dielectric capacitors. Is it possible to create an internal electric field in each electrode which would have an ...
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1answer
39 views

Question about capacitance on a double cylinder [closed]

I had an exercise that I am struggling to solve, I have 2 concentric metal surfaces with $R_1= 1 \,\text{cm}$ and $R_2 = 2 \,\text{cm}$. The cylinders have infinite extension along the direction ...
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1answer
97 views

Capacitance of spherical capacitor when inner surface of outer sphere is earthed

Let there be two concentric shells in which the outer sphere contains charge Q1 and inner sphere contains charge Q.Capacitance of spherical capacitor when the inner surface of the outer sphere is ...

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