Questions tagged [capacitance]

The ability of an object to store electric charge.

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24 views

Can Toroidal High Voltage Capacitors Cause Time Dilation?

I read in NASA's Warp Mechanics, they managed to warp space time with a high voltage toroidal capacitor, as detected by an interferometer. So I was wondering, is it possible to dilate time with this ...
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Reverse $\displaystyle v(t)=R\,i(t)+L\,\frac{di(t)}{dt}+\frac{1}{C}\,\int_0^ti(\tau)\,d\tau$ as function of current?

Consider the electrical circuit equation written as $$v(t)=R\,i(t)+L\,\frac{di(t)}{dt}+\frac{1}{C}\,\int_0^ti(\tau)\,d\tau \tag{1}$$ where $v(t)$ is electrical potential, $i(t)$ is current, $R$ is ...
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Practical capacity of a plate and a spherical capacitor regarding charge distribution

I want to ask if it could be true that the negative charge on a flat capacitor plate forms a ring distribution as they are repelling each other and does this fact have as a consequence that a ...
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What is The ratio of the charge $Q_4/Q_1$ across the capacitor below? [closed]

What is the ratio Q4/Q1 of the capacitor below if the church across C1 is q1 and that across c4 is Q4. my answer is 4 but I'm not sure if it is correct. Somebody please help
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Capacitor microphones for recording studios

This question is formulated exclusively for high school students precisely to interest them in a more concrete way. Condenser microphones are characterized by a capsule that functions exactly like an ...
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73 views

Why does the voltage goes away in my leyden jar?

This question is similar to this one in the sense that I have my amateurish Leyden jar and I'm supplying ~7.5v from 5 batteries (~1.5v each) in series. Some details and facts after experimenting: ...
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Equation for total capacitance of the tline unit cell

Is there a simple equation to express the total Capacitance of this differential line? I am not sure how $C$ and $C_m$ are related to the final equation $C_{total}$.
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1answer
37 views

What does complex permittivity mean?

I have been trying to solve the following question: $U(t)$ has the frequency $\omega$. Without an electric, the Voltage drop around the resistance is $U_R$. When half of the capacitor is filled with ...
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1answer
33 views

Would electricity be able to make a gamma ray?

I read that lightning creates gamma rays, but i'm not sure if it would be possible to have a capacitor that powerful to make a gamma ray. If this is possible, how efficient would such a process be?
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For capacitors, why does the dielectric need to be inserted at a small constant speed?

Likely a very silly question. I am aware that there is an attractive force from a charged parallel-plate capacitor in an open circuit without battery pulling the dielectric in, and that a decrease in ...
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58 views

Direction of electric field at points on boundary between two dieletrics

I am ripping my hairs trying to understand this answer, it is written that, for the following set up of two capacitor plates separated by distance $d$ and area $A$ with three dielectrics insert with ...
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Capacitor-spring analogy

Imagine the two terminal of a parallel-plate capacitor are connected to the two terminal of a battery with electric potential difference $V$. The capacitance of the capacitor is $C$, the area of each ...
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2answers
56 views

Stored energy of a capacitor

Imagine the two terminal of a parallel-plate capacitor are connected to the two terminal of a battery with electric potential difference $V$. If the capacitance of the capacitor is $C$, and the area ...
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3answers
784 views

Equation of capacitance of a capacitor

Imagine the two terminal of a parallel-plate capacitor are connected to the two terminal of a battery with electric potential difference $V$. If the capacitance of the capacitor is $C$, and the area ...
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1answer
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Polarity of induced EMF in an LC oscillator

The image given belongs to my textbook (NCERT Grade 12, Chapter-7, Alternating Current, Pg No 255): For your reference, this is the paragraph adjacent to the picture. I believe that the polarity of ...
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1answer
69 views

What is the capacitance of this capacitor?

Q: A thin metal plate P is inserted between the plates of a parallel plate capacitor of capacitance C in such way that its edges touch the two plates. The capacitance now becomes? \ My thoughts: We ...
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1answer
48 views

Why can't only one plate of a capacitor get charged?

In the above image, one capacitor is uncharged while the other is at a potential Vi. If we close the switch then potential difference across both capacitor would become equal(because the upper and ...
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Force on dielectric

I have been taught that the magnitude of the force on a dielectric is $$F=\frac{bε_0V^{2}}{2d}\left(K-1\right)$$ where: b is the width of the plate. $V$ is the EMF of the cell to which the capacitor ...
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What happens if you use a battery to charge up a capacitor fully, and then disconnect the battery, where does the charge 'go'?

The title says it all really, but I think that since the battery is disconnected there is now an 'open circuit'. I know that charge can only flow if the circuit is complete (closed). But the part that ...
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2answers
51 views

Capacitance of a system of spheres

Consider a system of two conducting spheres, as follows The outer sphere contains a charge $+Q$ and the inner surface is neutral. What would be the capacitance of the system? We know $C=\frac{q}{V}$....
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3answers
44 views

Deriving the equivalent capacitance in a series circuit formula

When we derive the formula for the effective capacitance in series, we say: $$Q/C_{eqv} = Q/C_1 + Q/C_2 + Q/C_3$$ (if there were 3 capacitors in this case). We would then cancel $Q$ to obtain the ...
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Interpretation of Poynting Vector

Short Version How exaclty can the Poynting vector be physically interpreted for static electric and magnetic fields? I know that it describes the magnitude and direction of energy flow in EM-waves. ...
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1answer
54 views

Do the conductors need to have equal and opposite charge necessarily to form a capacitor

In my textbook, it is written that In capacitor two conductors have equal but opposite charges. Is this always true? Why does it have to be like this? I have seen a few problems in which the ...
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28 views

Are Idealized Transformers Realizable?

Since parasitic capacitance in an inductor is always in parallel with its inductance, would this effectively become analogous to magnetic remanence exhibited within rebars (made from carbon steel) ...
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1answer
47 views

EMF in an LC circuit

What is the emf of the inductor in an LC circuit that is oscillating at a fixed amplitude, without damping, and without an external energy source? Am I right that the emf is zero when the work done by ...
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1answer
58 views

Can a capacitor with a fixed plate overlap area and separation have a maximum amount of charge it can hold?

Can a capacitor with a finite plate area and plates' separation have a saturation point of charge it stores, assuming that the dielectric does not break down? If there is, what formula can be used to ...
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1answer
33 views

How to derive second-order approximation of capacitance of parallel cylinders?

Given two infinitely long perfectly conducting cylinders of radius $r$ with centers separated by $d$, what is the capacitance between them, without assuming $d \gg r$? I'm familiar with the derivation ...
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Confusion regarding charge on capacitors

While I was studying about capacitors I realized that charge on the outer surface of the plates is zero when both the plates are given equal and opposite charges. Now mathematically, this realization ...
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32 views

Why isn't water thermal capacity used to easly cool the air in a room?

Why isn't water thermal capacity used to easly cool the air in a room? Would it be energetically cheap to use cold water as a room air cooler and when the water temperature reaches some limit it is ...
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1answer
55 views

Does making a conductor spiky increase its capacitance?

I'm thinking of the proofs for "charge accumulation at the points of a spiky conductor" e.g. https://www.feynmanlectures.caltech.edu/II_06.html 6-11 If charge accumulates at sharp edges, I'm ...
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Would the electric force on electrons be larger if the neutrons were polarized by protons inside the core instead they weren't polarized?

Would the electric force of the nucleus on electrons be larger if the neutrons were polarized by protons, compared to if they weren't polarized? Would neutron polarization add some extra force acting ...
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53 views

Self-energy of an infinite conducting charged plate

When we write the energy loss due to closing the switch in an $RC$ circuit, we find the difference between the initial and final energies of interaction between the two plates of the parallel plate ...
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Area of reference to find magnetic field inside a (dis)charging capacitor

Faraday's law of induction can be expanded:$$V=-N\frac{d(BA)}{dt}$$ and for a circuit which creates an area between the wires if that area doesn't change then it becomes $$V=-N\frac{dB}{dt}A$$ The ...
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Why is the electric field of a dielectric in a capacitor not just cancelled out outside?

As far as I know, a charged plate capacitor produces an electric field between the plates but outside the plates, the fields from the two plates as opposite just cancel out. If we can imagine a ...
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68 views

Please help me in this question about Capacitance? [closed]

I know its old but still I have 3 doubts... First: Suppose a charged capacitor is connected to an un charged capacitor as in image Now I know there is a flow of charge from C1 to C2 due to difference ...
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3answers
86 views

Why doesn't charge escape from capacitor?

A charged spherical capacitor kept in air do not loose charge because air is a bad conductor and increase in charge results in Corona Discharge. Is it because the nucleus of air molecule repels the ...
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Significance of resemblance of Electrical energy with Potential energy of spring

In a spring-mass system the total mechanical energy is represented as: $TE= 1/2kx^2 + 1/2mv^2$ $k$ being the spring constant and $x$ being the displacement. In L.C Oscillations we find the total ...
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Why are dielectrics used if they reduce the energy density?

Capacitors are used for storing energy and dielectrics are used to increase their capacitance. But a dielectric of dielectric constant K reduces the energy density of a capacitor by a factor of K. We ...
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Why is the electric potential for a point charge is $V=kQ/r$ but for the capacitance of parallel plate , the electric potential is $V=E*D$? [duplicate]

From what I've learned since now, I always knew electric potential is inversely proportional to radius or distance for a point charge, but I've come across the electric potential in a parallel plate ...
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The difference between $V=kQ/r$ and $V=ED$ ($V$ is electric potential)? [duplicate]

I realize $V=kQ/r$ is the electric potential of a point charge while the other one is the electric potential in a uniform electric field, but in the first case the distance (radius) is inversely ...
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1answer
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When calculating the pressure increment when a capacitor is submerged underwater why do we take force as +dU/dx? [closed]

For the following question (working attached), the solution given has (k-1) instead of the (1-k) in the numerator of my answer. Can anyone elaborate on what I might be doing wrong in this question. ...
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Is this a Dirac delta function in disguise?

Consider a typical detector equivalent circuit, where the detector can be seen as an ideal current generator $I(t)$. Since $I = I_C + I_R$ (currents through the capacitor and resistor), $I_R R=V$ and $...
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Does a wire cut at a place work as a Capacitor?

Suppose we have a electric wire with a battery connected to the two terminals of the wire. If we cut the wire at a place and separate the two terminals (having small cross sectional area) at a very ...
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44 views

How are the two arrangements equivalent?

An intuitive or a mathematical answer would do! Apparently the two arrangements are equal. How is it so? I'm new to this topic and my teacher bombarded us with such a statement with no explanation ...
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1answer
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Determining the capacitive reactance of a capacitor graphically

I measured the voltage and current of an RC circuit with the frequency of $f=105 \;\text{Hz}$. I modified the current with a decade box and measured the voltages ten times. With these measurements I ...
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1answer
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I dont really understand the question [closed]

A series circuit with a resistor and a capacitor has a time constant of 0.25 ms. The circuit has an impedance of 350 Q at a frequency of 1250 Hz. What are the capacitance and the resistance? I cant ...
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Capacitors and Kirchoff's Voltage Law

If we connect capacitor to voltage source, its voltage will be equal to voltage of the source when capacitor is fully charged due to Kirchoff's voltage law and no current will flow in a circuit any ...
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What is the equation for the electric field made by a capacitor?

In a capacitor, how can I calculate its electric field?
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How to find out resonance frequency of micro-resonators?

I am a student with a theoretical background, so I'm not well versed in the practicals. I have, on a silicon chip, a vacuum gap capacitor of Nb of 5 microns x 20 microns dimensions with 500 nm gap ...
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1answer
41 views

What is the charge of each plate? [closed]

One of the plates is connected to 5v, and the other is earthed. The distance between them is 5cm, and they each have an area of 3cm squared.

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