Questions tagged [capacitance]

The ability of an object to store electric charge.

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7 views

How to apply Gauss's law when dielectric constant in a capacitor varies continuously?

Let's say the problem is to compute the capacitance of a cylindrical capacitor with a dielectric material between the plates. The capacitor is considered to be long enough to ignore end effects. The ...
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Capacitance of a system of metallic plates

The question states: Four identical metallic plates are arranged in air at the same h from each other. The outer plates are connected by a conductor. The area of each plate is equal to S.Find the ...
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2answers
386 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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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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28 views

Surface charge on dielectric interface

What I have in mind is a system that consists of a capacitor filled with two dielectric materials, one of them with dielectric constant $\kappa_1$ and the other with $\kappa_2$. The capacitor is ...
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Resonant Circuits [closed]

So I have this circuit which is resonating, and I want to know how to calculate the output voltage, does anyone have any ideas on how to do this?
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Magnetic Field in a Leaky Capacitor

Consider a spherical capacitor which is made of two concentric spherical shells. The capacitor is charged so that outer shell carries a positive charge and the inner shell carries a negative charge of ...
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1answer
42 views

How is dielectric constant both $E_{net}/E_o$ and $ε/ε_o$?

The questions asks that, given the (surface) charge density (σ) on the plates of a parallel plate capacitor and dielectric constant (k), what would be the magnitude of induced charge density on the ...
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Grounded/Earthed electric circuits

I have a problem here that involves a circuit that is grounded at the point shown at the bottom the circuit. The units marked with C are all capacitors and Uv is a voltmeter. I haven't seen any ...
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1answer
256 views

Gain as a Function of Frequency (RC High Pass Filters)

I configured a simple series RC circuit. Across the circuit I have placed the terminals of a sinusoidal AC voltage source (I'm using my phone as a function generator). My goal has been to measure the ...
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The volume enclosing the charge in Gauss's law: does it have to be simply connected?

I was trying to apply Gauss's law to a simple problem: Find the capacitance of a cylindrical capacitor. Inner radius is $a$ and outer radius is $c$. The space between the plates is a dielectric ...
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I have derived that the impedance of a capacitor varies with time

For a closed electrical circuit comprising only an alternating current generator and a capacitor, I have derived that the ratio voltage/current of a capacitor is not constant. As Wikipedia defines it, ...
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Potential with plates at $V$ and $-V$

Consider two very large plates, one of which is lying on the $xz$ plane and sitting at a potential $+V$, and the other forming an angle $α$ with the aforementioned plate, attached to the other at the $...
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Analog of harmonic oscillation to electrical circuit

Equation of a damped harmonic oscillator under varying force $F$ is: $$ m\dfrac{\mathrm{d}^2 x}{\mathrm{d}t^2}+\gamma m\dfrac{\mathrm{d}x}{\mathrm{d}t}+Kx=F $$ And the electric analog to this is: $$ L\...
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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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Charge Redistribution on Capacitor Plates

Say, I've got two Large Conducting Sheets (intention : to neglect end effects). My question is quite fundamental and relies on the basic understanding of Charges. Now, I bring these two plates ...
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1answer
204 views

RC constant in a coaxial cable

i have a problem with understanding a certain aspect of calculating the RC constant in a coaxial cable. Given the reistance in the inner wire, and the outer wire, and given the capacitance. These ...
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1answer
355 views

Insertion of current carrying metal sheet between the plates of parallel plate capacitor

A parallel plate capacitor with area of plates A and distance between them d is charged with Voltage V1. A metal sheet carrying current is inserted between the sheets. How does the system change? What'...
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Liquid rising in a capacitor

Different authors of books have given two different answers which one is more appropriate? Q-A parallel-plate capacitor is placed in such a way that its plates are horizontal and the lower plate is ...
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Dual finite parallel disk capacitor; estimating mathematically that the potential or field or distribution is nearly uniform from first principles

Working through Purcell. In particular, doing my best to put everything on a firm footing, mathematically, so that I can understand it. But, I have struggled all week in establishing from first ...
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Redistribution of charges when capacitors are connected in series

This question is asked before but I didn't get the answers It is known that when 2 unequally charged capacitors are connected in parallel then the charges redistribute themselves till the voltage ...
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2answers
160 views

What causes resistance when moving parallel plate capacitor plates?

The electric field is perpendicular to the direction of the movement, so the vector product is zero, and thus the force should not exist. What causes it?
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How to find the transfer function for steady state? [closed]

I can not find the transfer function for sinusoidal input could you please help me find out the solution or at least where to start! i have found the transfer function Vo(s)/Vi(s)=1/(2j+1) but still ...
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1answer
814 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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Confusion about Electric Permittivity

I have learned about electric permittivity in two contexts: How much a medium reduces the strength of the electric field (Like if I have a charged ball inside a vat of oil, the oil will polarize and ...
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2answers
53 views

Electric field between two conducting plates both with zero potential and volume charge density between them

The questions says that two very large, conducting, parallel plates separated a distance $2a$ contain a uniform volume charge density $ρ$ between them and they both have zero potential, the ...
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1answer
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Why does this lightbulb glow faintly when I thouch it with my hand though it's not connected to the AC-source?

Take a look at these three pictures I made of one of our lightbulbs: The lightbulb is placed in a fitting which can be put directly in the power socket. In the first picture the bulb is turned loose, ...
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Energy dissipation due to displacement current

Consider the following problem: An isolated capacitor made of parallel circular plates of radius $a$ separated by a distance $d \gg a$ is charged such that there is a potential difference $V$ between ...
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Confused about a question on RLC circuits [closed]

Question: Find the current 'I' after a long time. I got that the answer is 2.66mA, but it is not the correct answer and I don't know why. There is no current on the capacitor after a long time because ...
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3answers
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How does a capacitor get charged instantly in AC whereas it takes infinite time in DC? [closed]

I have seen when a capacitor is connected to a dc source it takes infinte time to charge, but when connected to ac it takes the potential of the source instantly, probably the approach in the books is ...
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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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Which side of the capacitor is at higher potential?

Our physics teacher gave us a simple problem in our class related to the diagram below. The current increases at the rate $4 {\rm As^{-1}}$ and we are to find charge on the capacitor when current is $...
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Conceptual understanding of how a battery ensures that a capacitor has the same potential difference as it?

I was wondering how exactly a battery is able to ensure that a capacitor connected to it would have the same potential difference as it. Like, thinking about a battery similarly to a capacitor, I ...
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378 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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1answer
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How Are Electromagnetic Waves Produced?

How EM waves are produced say by a capacitor of an LC circuit here if $E$ is increasing in upward direction? My thoughts Thought 1:- If E is increasing E flux is increasing thus B field must be ...
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Sizing capacitor and power factor

The first formula is the reactance that you need to improve your PF to your desire (). The second formula given is use to calculate the capacitor needed to get the desired reactance (QVAR) I am ...
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1answer
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In a free underdamped RLC circuit, when the current is maximal, is the voltage in the capacitor zero?

I am in my last year of high school. We are studying free RLC circuits but we're not diving too deep into the theory. We know how to derive the differential equations governing charge, current and ...
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What is an isolated system in capacitive circuit?

Does isolated system here means that the plates of capacitor need not be connected to terminals of a battery?
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220 views

Cylindrical capacitor, why is the electric field radial between the two plates?

I'm trying to understand why if I consider a cylindrical capacitor whose height is $h$, the radii are $R_1$ (external) and $R_1$ (internal) and I put myself between the two plates I can say that the ...
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1answer
508 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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Charging of a capacitor by battery

I know that a battery does work when it takes positive charge from one plate of capacitor and deposits it to the other plate, thereby creating equal and oppositely charged plates having electric field ...
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How do measure the potential gradient between large capacitor plates?

I have built a capacitor for a biology experiment, but I need to measure the potential gradient between the plates. Mainly I am going to apply an AC current between the capacitor plates to have an ...
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Pressure increment in the gap between two parallel plate capacitors

What is the pressure increment in the gap between two parallel plate capacitors when they are immersed in water horizontally with a constant voltage of 500? Take dielectric constant = 81, distance ...
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Does sputtering Au on top of PEDOT:PSS thin film alter its properties?

I have grown thin films (~100-500 nm) of PEDOT:PSS by electrodeposition on top of thin films of Au (~1 nm) and now I want to measure the impedance of the PEDOT:PSS thin film. To accomplish this I am ...
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$LC$ in parallel with $R$ circucit resonance

I've been doing an experiment which involves measuring the voltage across the capacitor at different driving frequencies. Consider the circuit below: A sketch of the experimental curve $(R_1<R_2&...
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143 views

Capacitor Discharging through a fixed resistor

When a capacitor discharges, the pd across it goes from V0 to 0 in a given time. But when you look at the pd across the fixed resistor, this too decreases from V0 to 0. So we can say Vcapacitor=...
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MOS-Capacitor Work function calculation. Units don't match. What am I missing?

I am currently doing some lab work and I am stuck at a single equation that doesn't make any sense to me. I am given the following formula for the work function of Silicon: $$\Phi_{Si}=\chi_{Si}+\frac{...
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880 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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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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776 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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