Questions tagged [capacitance]

The ability of an object to store electric charge.

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Proof of continuity of voltage across a capacitor

It is known that the voltage drop across a capacitor is a continuous function of time. This means that, for each instant t0, we may write: V(t0-) = V(t0+) This relationship is very used in the time ...
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How to find the change in capacitance with moving dielectric? [on hold]

I am trying to find the change in capacitance, when the capacitor plates are kept equal and the same size and the distance kept fixed. But only the dielectric moves between the two plates. The goal ...
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Understanding simple LC circuits

I'm trying understand the physics of simple inductor-capacitor circuits such that there is just an inductor L and a cacpacitor C and a switch. Imagine first that the capacitor is fully charged and ...
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40 views

Nature of induced magnetic field lines in cylindrical capacitor

What is nature of the induced magnetic field lines inside a cylindrical capacitor which has a time variant potential gradient across it? For a parallel plate capacitor, its straightforward: the ...
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1answer
36 views

The energy stored in capacitors in series

If there is a capacitor of $2$ micro farad and $0.5$ micro farad in series and the charge on the combination of the two capacitors is $0.8\times 10^{-6}$ C. How would you find the energy stored on ...
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74 views

Some confusion regarding RLC circuits

I'm a mathematics student, and it has been years since I last did current/voltage/resistor related subjects in high school. However, for one problem that I've encountered, I actually need to calculate ...
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How does a capacitor charge if there is zero voltage across it?

From what I understand, a resistor causes a voltage drop. So it would seem that the end of the capacitor attached to the resistor would have the same voltage as the end attached to the battery. If ...
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1answer
13 views

What is the reference potential when considering electric potential on a body in case of self capacitance?

I was taking a lecture on self capacitance and the word 'potential of the conductor' came up. Now, self capacitance is for isolated conductors. From what reference is this potential measured?
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Determining the relationship between plate separation distance and capacitance experimentally

On a lab I recently did, I measured the capacitance between aluminium foils over a range of distances. One of the subsequent questions was to determine the function that best describes the ...
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16 views

Charge stored in a capacitor with dielectric when relative permittivity varies

Suppose the relative permittivity of the dielectric in an uncharged capacitor of capacitance C varies with the voltage applied, e.g. k=xV where x has dimensions of V^-1 (After this capacitor is given ...
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1answer
31 views

Difference between discharge tube and capacitor

I did search this on google but didn't get satisfactory results. Can you tell me difference between capacitor and discharge tube? "**Discharge tube has its gaseous medium at very low pressure but ...
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1answer
18 views

Inductor behaviour in LC oscillation [closed]

I want to ask that in LC oscillation , when the capacitor is discharging then on other side the current is increasing in inductor do inductor should act means it should oppose the current ....as same ...
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4answers
46 views

Can a series of capacitors convey alternative current?

Since capacitors allow charges to pack on the negative plate, there is some current flowing for a short time. Also the dielectric does not prevent the EMF otherwise there would be no voltage at any ...
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Can one assume during the discharge of lightning, some energy is dissipated as heat? (High School Physics)

I was doing homework, and the following appeared as a question: A negatively charged thundercloud above Earth's surface may be modeled by a parallel plate capacitor. The lower plate of the ...
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Paradox on setting up charges on capacitors

Staring with facts, 1)For a current to flow there must be a closed loop. 2)For a capacitor to be charged there must be a potential difference across it, 3)And obviously a charge must be transferred ...
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Potential and work across capacitor-battery circuit

Suppose, we have a simple capacitor/battery setup like that shown below. The battery is used to charge up the capacitor. After the capacitor is charged, there will be equilibrium, the field of the ...
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2answers
48 views

Parallel plates capacitor, boundary conditions (paradox?)

Given a parallel plates capacitor with two dielectric as shown here: (dielectrics stacked in parallel). It's usually stated that the field is given by: $\vec{E}=\sigma/\varepsilon_i \hat{z}$ ...
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1answer
52 views

Phases of current and voltage

Why $u(t)$ and $i(t)$ are in the same phase in a resistor, but in a condensator $i(t)$ is ahead of $u(t)$ by $\pi/2$, and vice versa in a coil? Note: I need physical explanation, like main reason of ...
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Why is a piezoelectric material a capacitor?

I am reading about piezoelectric elements and I am not sure why a piezoelectric material is like a capacitor. So a mechanical stres on the material will displace the electric charge distribution ...
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1answer
43 views

Why does the charge required on each plate of a capacitor to maintain a certain voltage decrease with the distance between the plates?

The $Q$ charge and the voltage $V$ of a capacitor are linked by $$Q=C\times V$$ For a parallel plate capacitor $C\propto \frac{1}{d}$. This implies for a given voltage $V$ between the plates, the ...
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1answer
45 views

Why is the information of a time delay missing in formulae of voltage drop across elements when we emulate DC with an AC voltage supply?

In an AC circuit, the reactance of capacitive and inductive elements are determined by the frequency of the AC signal. When we try to emulate DC analysis by putting $\omega$ = 0 , the capacitive ...
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1answer
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Capacitance and energy transfer [duplicate]

Capacitors: Using direct current I apply a voltage, $~V_o~$, to a capacitor of capacitance $~C~$. It acquire a charge of $~Q_o~$. I remove the charging source and I connect both sides of the ...
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2answers
47 views

Energy in capacitor [closed]

When connecting a capacitor to a battery, the battery works to put charges on the capacitor’s plates. First there is no charge on the plates, and battery does 0 work. Why, when the battery puts the ...
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1answer
47 views

Current in RC circuit

Why is current drawn in an RC circuit (in a circuit powered by DC voltage supply) independent of the capacitor used? While the capacitor is charging current drawn from the battery only depends on ...
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1answer
49 views

Why is the electric field of a conducting sheet of charge double the electric field of just a sheet of charge?

I was reading Feynman's Lecture on the Application of Gauss' Law and I came across this: Source This really confused me. What are the "other" charges he talks about? How does the additional field ...
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36 views

LCR circuit (AC source) potential difference across capacitor

For a LCR circuit connected to AC source of emf$$E= e\sin(ωt)$$ and let the current in LCR circuit be I then $$I=i*\sin(ωt+Φ)$$ then it is given that potential drop across the capacitor is V.ie$$V=-...
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105 views

Why don't capacitors hold charges on the outer walls of the plates? [closed]

Suppose I have two metal plates in a vacuum and I give this system some electric charge,the charge would distribute itself according to Gauss law on both the inner and outer walls of both plates...but ...
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Force of attraction in capacitor [duplicate]

In a question, it was asked the force of attraction between the plates of a parallel plate capacitor. and it was solved as $$\frac{(1)(C)(V^2)}{2}=(F)(d)$$ $$F=\frac{(1)(C)(V^2)}{(2)(d)}$$ and I ...
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25 views

Why are the times at which max rate occurs different for the energy of a capacitor and the battery

When charging a capacitor the rate at which the battery provides energy is maximum at $t=0$ but the time at which the rate of increase in the energy of a capacitor is maximum is $t=CR\ln(2)$ (where $C$...
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3answers
360 views

What happens when electrons reach the battery?

We have a capacitor which is connected to a voltage source. The top plate of the capacitor is connected to the positive terminal of the source. Therefore, electrons go from the top plate to the ...
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1answer
42 views

Doubt in the derivation of Gauss's law in dielectrics

so in the 2nd page,when the dielectric material is introduced the gauss's law becomes $$\oint _ { S } \vec { E } \cdot \vec { d S } = \frac { ( q - q _ { i } ) } { \epsilon _ { 0 } }$$.But my ...
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72 views

Force in an isolated capacitor when a dielectric slab is introduced [closed]

my question is about capacitance: a dielectric slab is inserted between the plates of an isolated capacitor. The force between the plates will remain unchanged. how? I mean the knowledge I had gained ...
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71 views

Voltage propagation along a wire [closed]

Let's say you have a wire connected to a device that you can switch between high-voltage and ground voltage. The wire is not connected to anything on the other end. You're observing the voltage in two ...
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Why am I getting two different expressions for capacitance? [duplicate]

The question is: A capacitor of capacitance C1 is connected to a battery of potential V0. The battery is then disconnected and a second capacitor of capacitance C2 is connected to the first ...
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2answers
42 views

Capacitors connected in parallel with a switch attached [closed]

What does it mean when they say capacitor reaching equilibrium?
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160 views

Circuit - solve Kirchhoff's laws with determinant?

Here is an exercise from my textbook. ]1 At first I solve it by using Kirchhoff's laws directly and using complex impendance: $$U_{in}=\frac{1}{Cs}(i_1-i_2)+i_1R_1$$ $$0=R_2i_2+\frac{1}{Cs}i_2+\frac{...
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1answer
18 views

Electric potential difference between capacitor's plates, doubt about the sign?

I'm trying to solve a doubt that has taken me away way too much time and so I'm asking here. In our lectures we defined the electric potential difference between a point A and B as the line integral ...
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2answers
85 views

Applying Kirchhoff Rule to an LC circuit

In a simple LC circuit (just one capacitor and one inductor), using the Kirchhoff rule has $$\frac{Q}{C} + L\frac{dI}{dt} = 0.$$ But isn't the voltage drop across an inductor $-L\frac{dI}{dt}$? What ...
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53 views

Common potential in Capacitors

If two isolated charged capacitors (of different capacitance) are connected in parallel to each other they acquire a common potential. But suppose if i connect positive plate of one capacitor to ...
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13 views

Difference between Capacitor and a battery [duplicate]

Capacitor stores electric charge and battery also stores electric charge. SO whats the difference between them?
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1answer
43 views

Electric field between capacitor plates

When we try to find the electric field between the capacitor plates, what is the right way to do it? This is one of the ways I've seen and I don't understand why: Using a Gaussian cylinder on the ...
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21 views

Capacitance of insulated conductor with charge on insulation surface

I have an insulated wire at high voltage (10s of kV) running above a conducting ground plane. In my case, I expect that corona discharge will occur briefly after the HV generator is turned on, but ...
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3answers
51 views

RC Circuits- Charge and Energy

It takes longer for the charge in an RC circuit to fall down to half its initial value than for the stored energy. Why?
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1answer
42 views

Gauss's Law on Parallel Conducting Plates

I have a question regarding the application of Gauss's law to find the E-fields produced by two parallel conducting plates. My textbook (Halliday and Resnick 9e) states that there is no E-field above ...
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1answer
77 views

Why is neper frequency called a frequency?

In the context of complex frequency of RLC circuits, the real part is called neper frequency, according to units it's understandable that it has 1/s as the unit which is same as frequency but what is ...
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Passive heat shield possible to stabilize performance of high tempetature range supercapacitors on Moon?

On the Moon surface, the temperature can oscillate between -160°C and +130 °C. As I can see, there are high remperature range supercapacitors available to work between -55°C and +200°C. Research ...
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48 views

Heat developed in a circuit

Suppose I have a simple circuit with capacitors, a battery and a key. There Is a change in energy stored in capacitors when the key is closed. How will I find the heat developed in the system? Is the ...
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A relationship between parallel plate capcatior's capacitance & it's spacing distance

In my experiment class, I measured a curve between the parallel plate capacitor's capacitance and it's spacing distance. But the result is not very similar to expectation - despite the spacing ...
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1answer
33 views

How does charge movement vary between insulators and conductors?

I've been reading A Student's Guide to Maxwell's Equations by Daniel Fleisch, and he states: in nonconducting materials (called "insulators" or "dielectrics"), charge does not move freely, but may ...
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Rates of charging in an RC circuit when components are partly charged initially

Just to be sure of my reasoning I am describing a simplified version of my problem Two capacitors of capacitance $C_1$ and $C_2$ are connected in series to a battery of emf $V$ volts having some ...