Questions tagged [capacitance]
The ability of an object to store electric charge.
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How does charge flow (directions) from capacitors in this question?
A circuit is connected as shown in the figure with the switch S open. When the
switch is closed the total amount of charge that flows from $Y$ to $X$ is?
(A) $0$
(B) 54$\mu$C
(C) 27 $\mu$C
(D) 81 $...
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0answers
31 views
Spherical capacitor with dielectrics [closed]
Consider the following system:
which consists of a conducting sphere with free charge 𝑄, a dielectric shell with permittivity $\epsilon_1$, another dielectric shell with permittivity $\epsilon_2$ ...
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3answers
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Why are the two outer charge densities on a system of parallel charged plates identical?
One of the ways examiners torture students is by asking them to calculate charge distributions and potentials for systems of charged parallel plates like this:
the ellipsis is meant to indicate any ...
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Change in temperature of dielectric when capacitor is charged and discharged
Suppose I have a capacitor with a dielectric between its plates. Intially the temperature of dielectric is $T_{-1}$. The capacitor is fully charged and the temperature of dielectric is noted.. say, $...
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2answers
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Why do phasor derivations related to LCR circuits consider $V_c = I * X_c$ even if voltage and current are out of phase?
In a capacitor, the current leads by $\pi/2$. But even then derivations of of total voltage in LCR circuits using phasor diagrams assume that $V_{inst.} = I_{inst.} * X_c$
Where $V_{inst.}$ is the ...
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3answers
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RC circuit discharge while being connected to a battery?
I am facing a conceptual problem in analyzing the following situation which was part of a physics exam;
A series RC circuit with $R = 200k \Omega$ and $C = 10 \mu F$ is connected to a 5V battery and ...
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10answers
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Is every open circuit a capacitor?
I think that even open-ended wires can let AC current flow through them, just with a low capacitance. I also think an antenna could be a capacitor and open ended. Am I thinking correctly?
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Energy dissipated across a resistor when charging a capacitor
I am a beginner in Physics and I am a little confused about RC circuits. I am working on a project in which I am measuring the power loss from a resistor when charging a capacitor in an R-C circuit.
...
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Why do we change signs arbitrarily while calculating RC circuits formulas?
When I have to calculate the formulas regarding RC circuits, for example the process of charging a capacitor, there is a discrepancy between my calculations and those of all the books I can find.
Let'...
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2answers
36 views
Adding a capacitor in parallel improves power factor of an inductive circuit?
I know that to reduce power loss during transmission, we require a power factor as close to one as possible. This can be done by making $Z$ tend to $R$ which can be done by increasing $X_c$ such that ...
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1answer
42 views
Confusion with electric field in a capacitor circuit
I'm having a confusion involving a couple of laws for a capacitor:
$C = \frac{Q}{V} \propto \frac{1}{d}$. The capacitance, the amount of charge the capacitor can hold for a certain voltage between ...
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4answers
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Why do we use dielectric materials in a capacitor?
Okey first of I know dielectric materials used in capacitors to insulate and polarize due to electrical field created by two metal plates and then when you connect this stored energy to a system you ...
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3answers
33 views
About the capacitance of the capacitor
I would like to ask two questions here ,
1. When a capacitor reaches to its maximum limit charge starts leaking and it ionises the air atoms . Well is it true ? As I'm not able to get an convincing ...
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1answer
46 views
Capacitors between two batteries [closed]
The positive terminals of both batteries are supposed to be on the right side
Here I need to find the potential difference between the parts a and b.
What I did was I assigned charge $q_1$ to the $2\...
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0answers
19 views
What is the amount of work done by collapsing of two parallel charged plates?
I am trying to use integration on surface but am getting different results by Gaussian and Faraday laws. Let’s say two parallel plates with opposite charges of Q and distance of R collapse on each ...
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4answers
41 views
Find relationships between the voltage difference across capacitor and resistor
I'm trying to learn kirchhoff's law. but im stuck on how to solve for a circuit that has both a resistor and a capacitor. How would you proceed?
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1answer
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LC-circuit and the current
A capacitor and a coil are charged in the LC circuit. When the circuit switch is closed, the current starts to flow. In theory the oscillations and the current do not deteriorate, but why in reality ...
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3answers
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What does leakage of charge in plate and isolated spherical capacitors mean?
I've read quite a lot of times about leakage of charge in capacitors, but what does it exactly mean?
Do we see sparks? Or is it some current flow? Or something else?
Say I have a charged sphere, so ...
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2answers
56 views
Differential equations for the LC circuit
On wikipedia one can find that the DE for an LC circuit is given by $$\ddot I+\frac{1}{LC}I=0$$In one of my papers however I found the equation $$\ddot Q+\frac{1}{LC}Q=0$$ and I've been confused by ...
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1answer
56 views
Resistor Capacitor circuits
I am a high school physics teacher and came across some issues today that I am unable to explain.
We made a circuit with an $11$ V power source connected to a $100~k\Omega$ resistor and $100~\mu F$ ...
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2answers
64 views
How can AC current pass through an open circuit?
I think for example for oscilloscope what gets signal just in one wire and how can even ac go through only one wire?
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1answer
26 views
Resolve The Envelope Detector Circuit
I was working on a little project and I was wondering if the envelope detector circuit could be resolved analytically. Let me explain.
The circuit is the one shown above, I know the values of $C$, $R$...
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0answers
22 views
capacitance of cube skeleton
A cube of 12 capacitors is very common problem. find capaciance accross edges we get 12c/7.
But lets say we have 8 more capacitors involved now.
that is we have capacitors at all sides of cube and ...
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1answer
43 views
Is a radio receiver antenna a capacitor?
I think so, but its capacitance should be very small, so how can the antenna correctly receive the signal, the low capacitance wont bother the signal?
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1answer
36 views
Why is charge proportional to capacitance? [closed]
I'm having trouble understanding why the charge is multiplied by the dielectric constant in the following question:
A parallel-plate capacitor has capacitance C0 = 5.00 pF when there is air between ...
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5answers
80 views
Why is capacitance increased with a dielectric rather than reduced?
So conceptually, if a capacitor is connected to a voltage source, and if you decrease the distance between two plates, the electric field in between the plates increases. This means that you can hold ...
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1answer
33 views
How do you calculate the capacitance of a parallel plate capacitor with multiple dielectrics? [closed]
My question is how would you go about calculating the capacitance of a parallel plate capacitor which has two mediums in between the parallel plates. I am aware that for a regular parallel plate ...
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1answer
33 views
If voltage across a capacitor GROWS till maximum in finite time then, is it possible that the capacitor also reaches maximum charge in finite time?
When a dc-voltage V is applied to a capacitor C, the charge on it takes infinite time to reach maximum value ...
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1answer
80 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
51 views
Does an uncharged capacitor in a non uniform electric field have a voltage difference at its terminals?
If an uncharged capacitor was placed in a dc field would there be a voltage difference developed on its terminals related to the different locations of the two surfaces in the voltage field? Would the ...
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2answers
33 views
Charge decay (leakage) of a charged metallic sphere
I have a spherical ball (charged to a specific charge) and the charge on the ball leaks to the surrounding. I observe that the charge on the ball reduces exponentially. Can anyone give a theoretical ...
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2answers
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Can we define rms current for pure inductive and capacitive ac circuit?
For a purely inductive and capacitive ac(sinusoidally varying) circuit, average power dissipated across a capacitor or an inductor is zero. Then does that mean RMS current is zero?
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What happens to a system of capacitors when a dielectric is inserted into one of them?
sorry for my English.
While doing some homework I've stumbled upon this "circuit":
the system is connected to the same potential difference through a generator that is connected to points A and B.
...
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1answer
28 views
RC circuits - what can we interpret when the voltage across the capacitor is equal to zero?
When applying the law of addition of voltage in RC series circuit with alternating sinusoidal current, we notice that voltage across the generator is equal to the sum of the voltages across all other ...
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2answers
86 views
Common potential of two capacitors
I read in my textbook that when two isolated capacitors are connected to each other, redistribution of charge takes place in such a way that they both acquire a common potential. My question is why ...
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2answers
69 views
Current without EMF in AC capacitance circuit
In AC circuit with only capacitance, current in circuit is maximum at time t=0 but emf of source is E=0 at t=0 , how can this happen,
How can current flows without emf.
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2answers
62 views
Charging and discharging a capacitor [closed]
So from what I understand, in the case for the charging capacitor, I understand the voltage across the capacitor as well as the charge can be given as the function of time:
$$V(t)=\epsilon(1-e^{-t/RC}...
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2answers
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RC circuit confusion [closed]
I was doing some RC problems in A levels, and in ine of thr problems it was about a circuit attached as a picture:
My question is can someone clearly explain to me why when time goes to infinity , ...
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2answers
99 views
How is a capacitor implemented in Kirchoff's Loop Rule?
I'm real stumped here.
I may be missing something, but I'm genuinely perplexed as to how one would add a capacitor to the list of elements being added to an equation through Kirchoff's Loop Rule (KVL)...
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1answer
29 views
Ratio of charges between capacitors in parallel and in series [closed]
Context: this is a multiple choice question, but no explanation is given
Question: three capacitors of equal capacitance are connected in the following circuit. Determine the ratio of charge in ...
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0answers
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Is the permittivity of a dielectric medium measured by application of radio frequency of 1 KHz and a resonant circuit of 1KHz are same?
I am working on a procedure in which I assess the dielectric constant of a medium by subjecting the dielectric medium to electromagnetic radiation of certain frequency (or the medium is subjected to a ...
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1answer
73 views
How to differentiate Capacitance (Italized C) and Coloumbs (regular C) on paper [closed]
I am doing a question on capacitance and coulombs. I got the answer correct, but I was wondering how a physicist, when doing the calculation on paper, would differentiate a C and C?
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1answer
34 views
How to compute the self-capacitance of a conductive shape?
(Depending on the answers given, this question might be better suited for Math.SE, but I don't think so.)
I recently learnt about the notion of self-capacitance of a conductive shape, which now seems ...
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2answers
53 views
Question on capacitance
I am recently trying to learn electrics on my own but am a bit confused with regard to capacitance. By Gauss law, I understand that the electric field from a single parallel plate results in:
$$ E = \...
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0answers
95 views
Capacitance of spherical capacitor when inner sphere is earthed
Consider the following derivation:
(Source: http://www.ncert.nic.in/html/learning_basket/electricity/electricity/electrostatics/inner_sphere.htm)
If a charge of $+Q$ coulombs is given to the outer ...
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1answer
73 views
Partially Filled Capacitors
I know that, for partially filled capacitors, one treats the space between the capacitor plates as two or more capacitors either in series or parallel. However, I don't fully understand why the ...
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0answers
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rotating capacitor question
Imagine a simple setup.
I have a copper disc and another copper element held close to the disc at one of it's sides, this element is stationary but the disc is rotating, the part between the disc and ...
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1answer
60 views
Why do we not have devices like inductors or capacitors to hold gravitational field? [closed]
I know that a capacitor can store electric field and an inductor can store magnetic field. So is there a way that gravitational field field can be stored in any such device. Also we do not have a law ...
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2answers
51 views
Does the capacitance depend on the distance?
I know that the Capacitance of a capacitor does not depend on the Voltage (because it is a measure for how much charge a capacitor can hold) and it largely depends on the Area
i.e. it holds that : $...
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2answers
117 views
Van de graaff generator, Leyden jars and capacitance
How will the capacitance of a typical desktop van de graaff generator be affected when connected in series to a group of some 5-10 Leyden jars?
I know that the capacitance is decreased in series ...
