The ability of an object to store electric charge.

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1answer
38 views

Loading a capacitor in an RC circuit

I have an RC circuit to which I am going to apply voltages of 5V every 100ns. So every 100ns, the capacitor will change its "state" from charging up to uncharging. I have been trying to find the a ...
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0answers
23 views

Storing energy in cylindrical capacitor [on hold]

Calculate the capacitance per unit length of two coaxial cylinders, the outer one with radius $b$ and charge $Q$ and the inner one with radius $a$ and charge $-Q$. I found that the the electric field ...
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5answers
1k views

Is voltage always proportional to its derivative?

We write, because of Ohm's law: $$V=RI(t),$$ but also we have $$C\frac{dV}{dt}=I(t).$$ From the first equation we deduce that $V\propto I$ and from the second $\dot V\propto I$. So we can conclude ...
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3answers
69 views

I wonder why I cannot charge a capacitor with alternating current?

Why can't I charge the capacitor with AC? How do the plates block the flow of electrons with DC but not with AC. Somebody told me that the DC is blocked by the capacitor, so the capacitor gets ...
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0answers
36 views

Capacitance changes by a factor of 3 or 9?

This is an example problem with solution in a book I am reading on electrostatics. "We have two square parallel plate capacitors with length $a$ and separation $d$ with $d<<a$. If we triple ...
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0answers
30 views

Capacitor with big space of insulation and polymer inside

The capacitor has insulator and it is covered by two conductors from top and bottom. I started to think if this insulation part can be wide like 1 cm big - yes, it can but then permittivity has to be ...
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0answers
37 views

How can a paper battery behave like a capacitor?

I was trying to understand how paper batteries work and came across some explanations saying that the paper battery can also behave like a supercapacitor on account of its ability to discharge and to ...
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1answer
37 views

Capacitor-like-thing for controlling temperature of fluid?

I want to minimise the Gibbs' phenomenon like thing i.e. sudden peaks (temperature peaks here) in a container. Assume you have a cone where you want to block the transmittance of the temperature into ...
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2answers
32 views

Energy stored in a capacitor in an RC circuit

Suppose we have a capacitor of capacitance $C$ and a cell of emf $E$, why is the maximum energy stored in a capacitor equal to $\tfrac{1}{2}CE^2$? I feel confused because, the potential difference ...
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3answers
44 views

Energy stored in a capacitor

Suppose we have a capacitor connected in series with a resistor and this is connected to a cell. So would the voltage across the capacitor be less than the the emf of the cell? And hence the energy ...
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2answers
41 views

Can I calculate the current of any setup with capacitance by the same formulae?

There are known formulae relating a capacitor's voltage and current in its classic form (battery, wires, a capacitor circuit), but what if we had a charged plate (-ve), then we put on one of its ...
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1answer
41 views

Argument for symmetry of potential of a spherical capacitor filled with dielectric

A spherical capacitor with inner radius $r_1$ and outer radius $r_2$ is filled with dielectric material with permittivity $\epsilon=\epsilon_0+\epsilon_1\cos^2\theta $. $\theta$ is the polar angle. ...
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1answer
38 views

Why can rolled up capacitors be modelled as flat parallel plates?

If you have two parallel plate of opposite charge with a dielectric in between, then Capacitance, $ C = \frac{A \epsilon_{0}}{d} K$, where $ K $ is the dielectric constant. This is used to calculate ...
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1answer
80 views

How is capacitance of a cylindrical capacitor calculated?

I've just begun learning capacitance, and my lecture notes have a section on calculating capacitance for capacitors in vacuum of various shapes, e.g. two parallel plates and concentric spherical ...
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4answers
63 views

Why is capacitor used?

I don't quite get the practical use of a capacitor. The theory is fine, but in simple words please explain how, why and where capacitors are used? Is there any other equivalent circuit for capacitors? ...
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2answers
59 views

How to calculate the charge on a capacitor [closed]

I have a network in which $C_1$ ($8.73 \;\rm \mu F$) and $C_2$ ($2.46 \;\rm \mu F$) are connected in parallel and $C_3$ ($7.45 \;\rm \mu F$) and $C_4$ ($2.22 \;\rm \mu F$) are connected in parallel. ...
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2answers
38 views

Capacitor physics problem

I read in a book that if both the plates of a parallel plate capacitor are given equal positive charges q, then the charges on the facing surfaces will be zero and the charge on the outer surfaces is ...
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2answers
47 views

Principle of superposition for capacitor

In a capacitor the parallel plates of opposite charge create equal electric fields in opposite directions. We know field outside the capacitor is zero but inside the capacitor it is non zero. My ...
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1answer
21 views

Why is parasitic capacitance in inductor said to be in parallel?

Internal resistance of inductance (or other devices) are said to be in series. But parasitic capacitance is said to be in parallel (in case of an inductor). Why is that so? What determines whether an ...
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1answer
22 views

Help in Basics for Capacitance

How does capacitor store a charge? I'm a little bit confused, as I know that a capacitor stores charge but how does it do so?
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2answers
52 views

Basic of Capacitor

I've 2 capacitors; plate area, difference between plates and dielectric is same. Only thing is that the metal used in plates is different. Since the formula $\displaystyle C=\frac{\varepsilon A}{d}$ ...
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1answer
130 views

Why is $I_0\sin\left(\dfrac{\pi}{2}-\omega t\right)$ not used as a solution of the purely capacitive AC circuit?

Why is $I_0\sin\left(\dfrac{\pi}{2}-\omega t\right)$ not used as a solution of the purely capacitive circuit? My Research I've searched on Google, Phys.SE and many school level Physics books ...
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3answers
94 views

Capacitance: How to increase total charge drawn from a battery?

I can't seem to find any information about how parallel capacitors or capacitors in a series affect how much a capacitor can charge, not in my textbook or online. Here is the question I am trying to ...
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2answers
62 views

What will happen when “earthing” is not an option?

I know that earth has a very high capacitance (of about 711$\mu$F) and it would take a lot of time for this but since we earth almost all our appliances for safety, wouldnt one day come when earth ...
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1answer
152 views

Capacitor charging, work done by battery on changing polarity

A uncharged capacitor $C$ is connected to a battery with potential $V$. It becomes fully charged and has a charge $Q=CV$ stored on it. Now the polarity of the battery is reversed. The capacitor will ...
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3answers
93 views

Why does a $1/2$ appear in this simple capacitor equation?

The maximum energy stored by a capacitor is when it's (theoretically) fully charged or just before it reaches dielectric breakdown, if you will. It seems, then, that the maximum energy ($E$) $=QV$ ...
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3answers
123 views

Charge On parallel plate capacitor?

Suppose if we supply two plates of parallel plate capacitor with charges $Q_1$ and $Q_2$.What would be the charge of the capacitor? As the field inside plate should be zero and hence using gauss law I ...
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2answers
36 views

Charging a spherical capacitance

How could one charge a spherical capacitor with a battery or any other emf source?
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0answers
43 views

Does the Fringe effect occur in capacitors in the interdigitated form?

I am currently doing my undergrad dissertation on graphene supercapacitors. I have read that the fringe effect is a well established phenomenon on parallel plate capacitors, but does it also occur in ...
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0answers
49 views

Electric Potential Change

Imagine we have a conductor in the shape of a sphere with charge $Q$ on it. The conductor is not grounded. There is an associated potential $V=\frac{Q}{4\pi\epsilon_0 R}$ at and in the sphere, where ...
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3answers
41 views

Can the potential difference produced in Van De Graff generator used to generate electric current?

If this machine can build up high voltages of order of millions of volts, can we use this volt the generate current of electrons? The building up of potential difference can result in electric field. ...
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1answer
57 views

Application of Displacement Current

I'm reasonably happy with the derivation and results of displacement current, however, I'd like to be aware of a few practical applications of this idea. So far, the only one I'm aware of is when ...
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1answer
66 views

Energy conservation when capacitor charges in a zero resistance circuit

We know that when a capacitor charges from a source $E$, it stores energy of $E=\frac{1}{2}QV $. This is derived without taking into consideration any resistances present in the circuit. We also ...
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23 views

Breakdown voltage

Capacitor (Geiger counter) is made out of wire with radius $R_1 = 5 mm$ and coaxial tube with radius $R_2 = 5 cm$. What is the maximum voltage on the capacitor, given the breakdown voltage of air ...
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0answers
75 views

Charge distribution inside a parallel plate capacitor [closed]

I'm having difficulty deriving a known expression for the magnitude of the Electric Field within a parallel plate capacitor with applied potential difference $V$ and an immobile charge distribution ...
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4answers
169 views

What happens in a circuit, when the wire and the battery are superconducting. And shorted

When a wire with no resistance is connected to the terminals of an ideal battery, will a current exist in the circuit? If a capacitor is added to the circuit, will it be charged by the battery or will ...
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1answer
70 views

What is the correct way to take out equivalent capacitance here?

So here I have a capacitor with two plates , one positively charged and one negatively, as shown in the figure. Now the material between them is $k_1$ for thickness d/2 and $k_2$ for the other d/2. ...
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1answer
62 views

Three-plate capacitor [closed]

What is the total capacitance of this capacitor? Is it analogous to the case of inserting a plate into a capacitor (essentially creating two capacitors in series)?
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1answer
252 views

Wheatstone bridge Capacitor,Dead Capacitor [closed]

I want to know that if in a Wheatstone Bridge ,that is made of capacitors only we have this condition $c_1c_3=c_2c_4$. The $c_5$ capacitor would be dead and it's voltage would be zero? Actually I ...
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0answers
45 views

What is a non-linear capacitor?

I'm new here. I have a (maybe dumb) question: What are non-linear capacitors? I'm given a circuit including a capacitor and the question says The given capacitor is non-linear with the ...
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1answer
103 views

Kirchoff's rules and RC circuits [closed]

You can view the image bigger: http://i.stack.imgur.com/4moUP.png I'm studying RC circuits and I can't understand the part when we use Kirchoff's rule. When working with batteries, when we're ...
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1answer
172 views

What is the capacitance of parallel plate capacitor with different electrode material?

What is the capacitance of parallel plate capacitor with different electrode material? The capacitance of parallel plate capacitor depends on dielectric material, surface area, and separation between ...
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1answer
63 views

Energy Stored in a Capacitor with and without Dielectric

I have seen the equation $V = \frac {V_0}{K}$, but also the equation $V=\frac{1}{2}CV^2$. The values of C and V increase in the same linear ration with K (because $C=KC_0$). However, as the energy ...
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2answers
175 views

Simultaneous Charging and Discharging Capacitor

sorry if I sound little noobish. Though I have a fairly good understanding of physics, I sometimes don't understand the electrical aspects. Say there is a capacitor. This capacitor is expected to act ...
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1answer
48 views

Charging a capacitor

Below is an excerpt from a physics textbook: One common way to charge a capacitor is to connect these two wires to opposite terminals of a battery. Once the charges $Q$ and $-Q$ are established on ...
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1answer
72 views

Capacitor with dielectric between the plates

Let's assume we have a capacitor of capacitance $C$ and potential difference $U$. After charging it we disconnect it. Then we put a dielectric between the plates. I know that capacitance will increase ...
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0answers
194 views

Power dissipated through resistor in RC circuit with charged Capacitor [closed]

so here's the problem: A simple RC circuit where the capacitor has been charged, and two resistors are in parallel configuration. How does one find the power (as function of time) through any of the ...
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2answers
97 views

capacitor in ac and dc circuits

In a dc circuit work done by battery=QV while energy stored in capacitor =(QV)/2 loss in energy=(QV)/2 While a capacitor in ac circuit has a no power loss.why is it so? Shouldn't heat be lost in ac ...
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3answers
284 views

Why do both plates of a capacitor have the same charge?

How do we know that both plates of a capacitor have the same charge? You could argue conservation of charge, but I don't see how conservation of charge implies the charge on both plates is the same. ...
2
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1answer
66 views

Capacitor in series?

Say you have two charged capacitors in series. Zoom in on one capacitor. For this specific capacitor, the charge on the two plates will be the same in magnitude, according to my textbook. My teacher ...