Questions tagged [capacitance]
The ability of an object to store electric charge.
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Current flowing in resistor after the switch is closed
I'm getting confused between the current flowing in $R_1$ and $R_2$ and the capacitor. Can someone elaborate on these questions?
ε1 =2.5 V / ε2=4.0V
C=22 microFarads
R1 = R2 = 1.5 ohms
Immediately ...
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What is the electric field between two conducting parallel plate capacitors?
Actually i am confused about the difference b/w electric field due to a non-conducting charged plate and conducting charged plate. And what should we assume when it is not mentioned that which plate ...
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1answer
25 views
How to calculate capacitance when inductance in known? [closed]
Below is the diagram (sorry for bad accuracy) that shows how current changes with time in LC circuit. On X-axis we have time measured in milliseconds (ms) and on Y-axis current measured in ...
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Find the The space density of the bound charges as a function of $\varepsilon$
Question: The gap between the plates of a parallel-plate capacitor is filled with isotropic dielectric whose permittivity $\varepsilon$ varies linearly from $\varepsilon_{1}$ to $\varepsilon_{2}\left(\...
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When a capacitor discharges in a simple RC circuit, is it treated as an active component?
While deriving expression for the voltage across capacitor in a discharging RC circuit, I stumbled across whether I should treat the capacitor as an active or a passive component(To properly apply the ...
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Need help understanding a statement about energy in capacitors
The electric potential energy stored in a charged capacitor is just equal to the amount of work required to charge it—that is, to separate opposite charges and place them on ...
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1answer
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Full capacitance matrix symmetry property - how to derive it?
In this excellent article, the author, in sec. 1.4 describes the full capacitance matrix properties.
He writes:
The capacitance matrix is symmetric: $C_{ij} = C_{ji}$. This is related to the fact ...
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1answer
46 views
Equivalent Resistance Across Capacitor in RC Circuits
I need to find the equivalent resistance of the circuit here in order to find time constant. I know that I should replace current source with open circuit, then we have this:
That 1k Ohm confuses me. ...
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2answers
58 views
Is the energy supplied to a capacitor by a battery the same as the energy stored by a capacitor?
If we have three capacitors in series, would the energy supplied to the system be the same as the energy that is contained in the equivalent capacitance of these three capacitors?
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Need help finding energy stored in a capacitor [closed]
We have this set up and i have already found the equivalent capacitance. But now i need to find the energy stored in the 54uF capacitor and i know we must use $U=\frac{1}{2}CV^2$ but im not sure how ...
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1answer
23 views
Discharging of a capacitor
Consider a charged capacitor with its positive plate holding charge Q. Now I join the capacitor to an circuit with resistance R . So the capacitor starts to discharge. Small charge $q$ flows out of ...
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2answers
40 views
Why is the electric potential across a capacitor zero after a long time?
I was just exposed to this concept in class, that the electric potential across a capacitor is zero after a long period of time, but it was never explained why. This is for an RC circuit.
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Charge redistribution in term of Force
Suppose two spherical conductors each with a different radius. Initially, they are charged independently up to charge $Q_1$ and $Q_2$. Now let's that they are connected through a wire. Then the charge ...
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3answers
39 views
Why capacitance is constant? [duplicate]
I am new to the field of electrodynamics and I recently came across the definition of capacitance as
$$C = \frac{Q}{V}$$
It is said that capacitance is constant, which implies that total charge of the ...
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0answers
35 views
Where does half of the work done in charging a capacitor is dissipated? [duplicate]
The energy stored in a charged capacitor of capacitance $C$ with $V$ voltage across it is:
$$U= \frac 12 CV^2$$
Whereas the work done in charging the capacitor is:
$$W= CV^2$$
This means that $(1/2)CV^...
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1answer
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Charge densities when placing a conductor or a dielectric material inside a capacitor
Assume there are two conducting infinite plates. They make up a capacitor - one plate has a charge density of $\sigma$ and the other has a charge density of $-\sigma$. Assume the charges on them are ...
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2answers
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In LC circuit, the EM waves specifically originate from where?
In LC circuit, we know that there will be charge oscillations, so emw will be produced. I just want to know emw will originate from where? Will it originate from within the capacitor?
Or will it ...
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1answer
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Working of Capacitive Accelerometer
I've been studying about capacitive accelerometers, and basically how they work is by detecting the change in capacitance or as a result of change in the distance between the conductive plates, small ...
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2answers
37 views
Why does force between plate capacitors not change when dielectric is inserted between them?
I was told in my physics class that the force does not change between the two plates but wouldnt the electric field not change between them bc it gets divided by the dielectric constant?Hence the ...
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4answers
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How to convince myself that capacitance cannot be a function of voltage?
My textbook states that:
...The capacitance $C$ depends only on the geometrical configuration (shape, size, separation)of the system of two conductors. [As we shall see, later, it also depends on the ...
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2answers
39 views
Charge as a function of time in an RC circuit
In my professors notes, there is a function representing charge in terms of time, however there is absolutely no explanation to why this function holds true. It seems like he skipped the whole part on ...
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2answers
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Electric potential and increased capacitance
I could really do with some insight into how the capacitance of a conductor increases when you bring another oppositely charged or earthed conductor near it. The explanation in my book is as follows:
...
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3answers
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Will the free charge density on a disconnected capacitor plate change if I insert a dielectric?
We have a disconnected capacitor having charge density $\sigma_{1}$ on its positive plate.
Now we fill it with a dielectric as shown.
Will the free charge density( the mobile charges on the ...
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24 views
Physical resistor and capacitor structure and boundary conditions
From this figure, this structure is composed of a cylindrical resistor and capacitor. I am tasked with finding the resistance and capacitance of the top and bottom components. The problem I am working ...
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1answer
28 views
How does the charge accumulate inside a parallel plate capacitor?
I couldn't properly understand, how is it so that if I have a parallel plate capacitor, in which one plate has $+Q$ charge and another has $-Q$ charge then all the charge on the first plate will ...
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1answer
46 views
Intuitive explanation for why voltage decreases as distance between charges decreases?
A uniform electric field can be set up as shown:
The force for a given charge will be constant anywhere in this field. However, as the distance from the charge to the oppositely charged plate ...
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2answers
55 views
Why does the capacitor charge through a resistor?
I was working on a question where there was a circuit and the switch was open, there was one capacitor and one resistor. It said: immediately after the switch is closed, what is the current in the ...
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2answers
35 views
Will energy in an LC circuit become 0 if its is disconnected when the capacitor is fully discharged?
In a recent test I had a question in which there was an LC circuit with an inductor a capacitor and a switch. According to the answer key
If switch is opened when capacitor is fully charged energy of ...
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1answer
40 views
Time Constant of a Capacitor in DC
I've just started studying Physics and I'm not sure how you're supposed to calculate the time constant of a capacitor when a direct current is applied. DC means that frequency equals = so the ...
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2answers
45 views
Hamiltonian of a quantum circuit including a diode?
The LC circuit has a Hamiltonian:
$$\hat{H}={E_L\over2} \hat{\varphi}^2 + 4E_C \hat{n}^2$$
where $\hat{\varphi}$ is the magnetic flux and $\hat{n}$ is the number of charge.
What is the Hamiltonian ...
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$1 \text{m} \times 1 \text{m}$ parallel plate capacitor at $300 \text{ kV}$
I have a parallel plate capacitor 1 m x 1 m that is to be fully charged to 300 kV. The distance between the metal plates is 3 mm; the inner surface of one plate is to be coated with 1 mm ceramic (...
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3answers
70 views
Why are the capacitors in this circuit in parallel but not in series?
In the circuit, the capacitors are said to be connected in parallel. Why is that so?
Edit: The switch will be closed and C2 is fully charged by C1 and no more current will flow between C1 and C2. The ...
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1answer
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Capacitors and how electrons flow given the electric field direction
My question is given that a capacitor creates a two charged sides, by the electrons jumping from one plate to another thereby making one having an excess of electrons making it negative and the other ...
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1answer
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Charge on the plate of the capacitor
I was reading parallel plate capacitors in my book today and there I saw that the battery provides +Q charge to positive plate and -Q charge to negative plate? But we know that only electrons can flow ...
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0answers
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How to solve circuit in static electricty? [duplicate]
I just found this question, but I don't know how to solve it. The question has a answer, but still it don't give me the formula.
the answer for numeber 1 is 0,0 a
for number 2 is 40
for number 3 is ...
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1answer
32 views
Maximum charge of a separate capacitor plate
Suppose we have an initially charged parallel plate capacitor, then we separate the plates so each plate has a positive and negative charge (I did an experiment, the plates hold the charge), I think ...
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4answers
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Experiment to show that current leads voltage by 90° in capacitor
I understand that current leads voltage by 90° in capacitor.
How does one show that it is true by an experiment?
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3answers
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Why changing the distance between two parallel plates capacitor will affect its charge?
I have a question that is bothering me, Lets assume that I have a parallel plates capacitor with distance $d$ between them. Now connect it to DC voltage source $V$.
according to equation $$V=\frac{Q}{...
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1answer
44 views
Can it be the some energy will remain after long time? Capacitors and resistors [closed]
My question is pretty simple, but I'll have to describe the problem in order to ask it:
We have a an RC circuit as we can see in the picture.
The given details are:
the resistance of the resistor $ R $...
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0answers
21 views
Dispacement current value through dielectric
Will the displacement current be multiplied by K when a dielectric is placed between the plates of a capacitor.
Will its value then be K times the value without dielectric.
Will it be still equal to ...
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0answers
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Why is the worst case input/output impedance of an $RC$ filter $R$?
I'm going through the Art of Electronics in my spare time, and I ran across a problem I've been scratching my head about for a few days. The book states that in the worst case for any $RC$ filter, the ...
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1answer
24 views
How exactly does a (capacitive) humidity sensor work?
How exactly does a humidity sensor work? For example, how can it differentiate between a relative humidity of 30 % and 35 %?
I know how a capacitance works but for me that principle is way too high ...
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2answers
91 views
What is the capacitance of a spoon?
Has anyone measured it? I can't seem to find anything online for "spoon capacitance"; what's the expected (self-)capacitance on the typical household utility metal spoon? The spoon heads ...
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1answer
29 views
Heat produced by resistor in a circuit with charged capacitor and no battery [closed]
C2 has a charge of 8C and 4F capacitance. C3 has no charge and 2F capacitance. S2 is then closed for a long time.
What is the total Joule heat generated in resistor R2?
The answer is 8J/3 but I'm not ...
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1answer
28 views
Why doesnt a capacitor discharge when you ground one end?
I have grounded one end of my capacitor after charging it but the voltage drops at a steady pace not as if it has lost charge. Is this because the opposing charges on the opposite plate are keeping ...
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1answer
51 views
What does electrostatic energy stored in a region mean?
Recently my teacher taught me about Energy density(Energy per unit volume) and told us the formula for the same.
This was explained by taking "Energy" as Energy of a parallel plate Capacitor ...
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1answer
35 views
Kirchhoff's voltage law for an ideal circuit containing only a capacitor
Let's say I have an ideal open circuit (i.e. there's no resistance in the conductors) containing only a charged capacitor and then I close it. Now, the charge on one end of the capacitor will move to ...
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1answer
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Kirchhoff's Voltage Law does not hold for a free source RC circuit?
Say I have a simple free source RC as depicted in the image below. The capacitor initially has a charge of Q on its positive plate and at time t=0 the switch is close. I use the mesh current as shown ...
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1answer
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Does the dielectric constant changes as the voltage is applied in every dielectric material?
As the voltage is applied at both sides of the dielectric material(ex. front surface +5V and rear surface 0V), the energy is stored in the material, right?
I heard it's because the dielectric ...
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1answer
35 views
New interpretation for Heat in Resistanceless Capacitive Circuits
I have been studying RC circuits and noticed that even in a resistanceless circuit, when a capacitor is charged by a constant potential difference source, there is considerable heat generation, equal ...
