Questions tagged [capacitance]

The ability of an object to store electric charge.

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29 views

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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3answers
94 views

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

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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1answer
981 views

Maximum current in LC Circuits [on hold]

Two capacitors of capacitance $C$ and $3C$ are charged to potential difference $V_o$ and $2V_o$ respectively and connected to an inductor, all three in series. Now the switch S is closed. Find the ...
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2answers
500 views

Current in discharging capacitor through fixed resistor?

In the textbook I'm using for physics it says that the charge left on the plates of a capacitor after time $t$, that is discharging through a fixed resistor, is $Q=Q_0e^{-t/\tau}$ where $\tau=RC$ is ...
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1answer
474 views

How to compute the charge as a function of time in a simple $CL$ circuit?

I am trying to compute $q(t)$ in a series circuit consisting of a capacitor of plate charges $q_0$ and $-q_0$ and an inductor. The switch is closed at time $t=0$. By Kirchoff's Law, $$\frac{q}{C}+L\...
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2answers
42 views

Energy in capacitor [on hold]

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
39 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
267 views

Capacitance calculation with numerical methods

For this structure (ellipse conductor covered with circle conductor. between them full of dielectric) I calculated electric field distribution with finite difference (Dirichlet problem for Laplace eq.)...
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1answer
34 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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1answer
45 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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A Simple RC Circuit [closed]

This is the most simple Rc circuit (i have just started learning) .My questions regarding this is- (This is a dc voltage supply) Will capacitor get charged by the potential drop of resistor or ...
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Engineering physics capacitor [closed]

A long cylindrical conductor has length 1m and is surrounded by a coaxial cylindrical conducting shell with inner radius double that of long cylindrical conductor. Calculate capacitance for this ...
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10 views

$C$-$V$ characteristics of MOS capacitors for different material [closed]

For C-V curve below for 3 different materials, (Si, InAs, InSb). What material will be corresponding to curve A/B/C? My understanding is that C is inversely proportional to the dielectric constant in ...
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18 views

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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2answers
168 views

Influence of an external electric field on an uncharged capacitor

Influence of an external electric field on an uncharged capacitor. Fig A shows an uncharged capacitor with no external electrical field. There is no net charge on each of the plates. Since the ...
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1answer
23 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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I got the answer but I suppose I did not understand the question very well [duplicate]

See as per the question, The Inductor pretty much will induce emf due to magnetic field and not due to other coil/current nearby. Thus I used $E= - d(phi(t))/dt$ as the induced emf. Then using (...
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3answers
345 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
39 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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2answers
316 views

Different charges of plates of parallel plate capacitor

Suppose the plates of a parallel plate capacitor have charges +2Q and -Q initially. Then if they are connected with a battery of emf V what will be the charge distribution on the plates of capacitor? ...
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1answer
455 views

Differential Equation Of Capacitor Energy In RC and RL Circuits?

I'm having a hard time finding the differential equation for enregy in a capacitor for an RC basic circuit which contains a resistor and a capacitor + the source . I have to start using the ...
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1answer
45 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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3answers
293 views

Potential difference across a capacitor

Look at the above circuit, I didn't get anything of it. Firstly i tried it using Kirchoff's voltage rule, I failed. I'm confused with those batteries. Can someone please explain me the role of those ...
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2answers
579 views

Charged dieletric/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 ...
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0answers
67 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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1answer
677 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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0answers
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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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1answer
414 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 ...
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2answers
876 views

Charging capacity and capacitance of a conductor

I know that charging capacity of a conductor is the maximum charge a conductor can hold And capacitance is the ability of a conductor to hold charge in a given potential . But how are these two ...
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1answer
748 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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2answers
193 views

One terminal of an ideal voltage source connected to earth->Massive current will flow?

Assume we have a "somewhat" ideal voltage source like a DC power supply powered by mains. Take just one terminal and form a conductive path between it and earth ground. Assuming that no conductive ...
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2answers
37 views

Capacitors connected in parallel with a switch attached [closed]

What does it mean when they say capacitor reaching equilibrium?
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131 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
695 views

Displacement Current Density of a parallel plate capacitor

Been stuck on this for a while and haven't been able to make sense of it. So let's say that we have a parallel plate capacitor with plate area, $A$, charging at a rate $i$. The gap between the plates ...
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1answer
121 views

fully filled capacitors with parallel dielectrics problem

consider that we have two dielectrics inside a capacitor as shown in the picture, let0s consider also that Q is the charge of the capacitor and d the distance between the two plates , the first ...
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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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1answer
118 views

Why is aluminium foil wrapped around a Leyden jar?

In the process of constructing a water Leyden jar, a foil of aluminium had to wrapped around the outside of the Leyden jar. What purpose does it fulfill?
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2answers
82 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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1answer
212 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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2answers
44 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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2answers
326 views

Current in a RC circuit

In order to find current in an RC circuit, resistance of only the resistor is considered i.e. $I_\text{resistor} = V_\text{resistor} / R$. Why is the reactance of the capacitor not considered? The ...
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5answers
56k views

What is the difference between a battery and a charged capacitor?

What is the difference between a battery and a charged capacitor? I can see lot of similarities between capacitor and battery. In both these charges are separated and When not connected in a circuit ...
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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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2answers
725 views

Why are the two sphere capacitors are said to be in parallel

When two metal spheres at a large distance are connected to each other by a thin conducting wire why are the two sphere capacitors are said to be in parallel and not in series?
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2answers
191 views

Trying to understand the electric potential and potential energy

I am trying to understand some facts on electrical potential and potential energy. It is quite confusing in the text to say that the zero potential could be freely chosen for convenience. In that case,...
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1answer
595 views

Why is work done against the electric field to move charges to charge a capacitor?

I'm a bit confused as to why there is work done against the electric field when charging a capacitor, as charge is moving from high potential to low potential. For the sake of this question, I'll ...
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1answer
37 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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1answer
137 views

Predicting voltages in RLC series circuits from AC source: differences in order?

Hoping this isn't too homework-like, but I'm missing some sort of concept here. Doing a lab, and I have to use previous data to predict the voltage across the 2nd and 3rd elements (e.g. order is LCR, ...
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1answer
177 views

Why can we consider two conducting spheres very far apart from each other as a capacitor?

If we have two conducting spheres of equal but opposite charge and they are at a large distance from each other, why can we consider this system as a capacitor? According to my textbook, this is valid....
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1answer
135 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 $t=18$ ...