The ability of an object to store electric charge.

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Capacitative energy of a general concentric shape of short separation

Consider a surface $\partial \Omega$ whose enclosure describe a three-dimensional shape $\Omega$ of characteristic length $L$. On this surface resides an inhomogeneous surface charge density $+\sigma(\...
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28 views

If iI have a capacitor connected to a battery can the negative charge be sent to an insulated object

If I have a capacitor permanently connected to a battery, that is lets say setting in a plastic bowl, and then run a wire from the negative of the battery to a non grounded object, say a metal can ...
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40 views

Average distance between electrons on a parallel plate capacitor

I came across this question in an old exam paper and I am interested in the way it was marked. The 'correct' answer doesn't seem to be as correct as it could be. Calculate the average distance ...
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1answer
48 views

Capacitance question

A capacitors capacitance, C is equal to Q/V right? If Q was somehow cut in half, would the potential difference also be cut in half, since V is directly proportional to Q? And if so, Its C would be ...
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111 views

Battery and charge separation

In this question : What is the difference between a battery and a charged capacitor? http://physics.stackexchange.com/q/32394 It is said that the battery does not have a charge separation on its ...
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2answers
186 views

Calculating effective capacitance of a circuit [duplicate]

Please refer to the image below. The question asks: 'The effective capacitance between terminals A and B in the network shown in the adjoining figure is?' Here is my working: (C5 and C6 connected ...
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2answers
98 views

Charges on capacitor after full charge by battery

When the charging is finished what will be the charge on an ideal parallel plate capacitor ? To be specific what are the charges on different faces of the 2 plates ? All the books say, after 100% ...
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1answer
17 views

Phase angle of a circuit

Above is the problem at hand. I know how to calculate the angular frequency and total impedance of the circuit given the information provided. However, I'm not really sure what the question is asking, ...
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3answers
810 views

Why do Capacitor Inductor circuits Oscillate instead of reaching equilibrium?

When the capacitor is fully charged there is a potential difference between its poles and that creates a current. This current would create a magnetic field that is changing in the Inductor (because ...
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70 views

Parallel Connection of Capacitor

Assume Two Capacitor filled with different dielectrics with dielectric constant $K_1$ and $K_2$ respectively in Parallel connection. Then we have same voltage $V$ on both capacitors. Therefore, $$\...
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1answer
82 views

Visualising current in the LCR circuit

I just went through the theory of the serial LCR circuit. There current and voltage are 90 degrees out of phase with each other. Now I was trying to imagine an animation with just dots. And I ...
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2answers
48 views

How is the capacitor affected?

I know that a capacitor stores electric energy or electric charge and understand how, but I don't understand how the distance and the voltage affects its capacitance (I mean what are the mechanisms ...
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1answer
1k views

Significance of Time constants in LR and RC circuits [closed]

What is the significance of a time constant in a circuit? Is there any use of knowing the time at which the charge in a capacitor is 1-1/e times its total charge? What is special about the capacitor ...
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69 views

How big of a capacitor would I need to release 5 amps for 0.2 seconds? [closed]

Just what the title says, 5 amps for 0.2 seconds. Please bear in mind that I have absolutely no grasp on electrical wiring, so I would appreciate simple terms. What I need to do is release a burst of ...
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1answer
45 views

Why is $k$ left out of the equation $C_\text{all} = (k\epsilon_0A_1/d) + (\epsilon_0A_2/d)$?

The capacitance of two capacitors in parallel is found using this formula: $$C_{all}=C_1+C_2 \, .$$ Capacitance is $$C=\frac{Q}{V} \, ,$$ and also $$C=\frac{kε_0A}{d} \, ,$$ so can I say $C_\...
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466 views

Capacitors in a series circuit with dielectric

When a dielectric slab is inserted between the plates of one of the two identical capacitors in Fig. 25-23, do the following properties of that capacitor increase, decrease, or remain the same: (a) ...
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1answer
100 views

Two capacitors in parallel vs series - electric field?

If we have two parallel plate capacitors in parallel, do the electric fields between their plates have to be the same? What happens if we have a coaxial cable of length $L$, which looks like this: ...
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1answer
63 views

What actually happens in a capacitor?

I have this doubt wandering through my mind for a long time. A capacitor, according to the definition of physics, is a charge storage device. In a simple parallel plate capacitor, when electrons ...
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55 views

Capacitors as Energy Wasting?

I am reading a lot of articles about capacitors as the energy storage. Let's consider simple circuitry which contain the battery and capacitor in series. The energy flow from the battery will be $E=\...
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1answer
253 views

Half wave rectifier at high frequency and small amplitude ac signal

This is the picture taken from my oscilloscope where I was just checking how a standard half wave rectifier properties. The yellow one is input signal of frequency 20.5KHz and peak to peak value is ...
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1answer
176 views

What happens when two charged capacitors are joined?

Two capacitors are charged and then they are connected with a wire. Then what will become constant after they are connected? Their potential or their charge? Exact question: A capacitor $2C$ is ...
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2answers
387 views

Derivation of capacitive reactance

Let $Q(t)$ be the charge stored in a capacitor $C$ in $t$ time for alternating current. Now, $$\displaystyle Q(t)=Q(0)+\int_{0}^{t}I(t)dt\\=Q(0)+\int_{0}^{t}I_oe^{j\omega t}dt\\=Q(0)+\frac{I_oe^{j\...
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1answer
50 views

Capacitors, Formula for Energy [closed]

I had a quick question; As you know there are three formulas for calculating the Potential Energy of a Capacitor U=Potential Energy $Q$=Charge $C$=Capacitance $V$=Voltage/Potential Difference 1) $...
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2answers
108 views

Why is an $LC$ oscillator lossless, but $C V^2 / 2$ energy is lost to a capacitor connected to an ideal voltage source?

It is mathematically proven that in an $LC$ oscillation that all the energy gets transferred from the inductor to the capacitor and vice versa. There is no energy loss as there is no load in the ...
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216 views

Energy loss in Capacitors

We have this formula in our textbook for loss of energy when two capacitors are connected together. They mention that it is due to heat dissipation. However, we have not considered any such term in ...
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403 views

Maximum limit of charging a capacitor

We say that we can charge a capacitor in proportion to the potential difference we apply across its plates and the maximum potential difference depends on the dielectric strength of the medium. Now ...
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175 views

Why is charge constant in series connections?

Why does each capacitor in a series connection hold the same charge? I understand that voltages and capacitances across capacitor plate pairs in series vary, but why is it a necessity that charge be ...
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1answer
37 views

Why a capacitor's potential increase until it is equal to the potential of the battery?

I understand that the potential between the plates of the capacitor increases as the circuit runs, but why it stops increasing exactly when it becomes equal to the potential of the battery?
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169 views

Why is the total potential difference in a circuit the sum of the individual potential differences?

I am having difficulty in applying my understanding of electrical potential to circuits. Why is the total potential difference in a circuit the sum of the individual potential differences among ...
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2answers
456 views

Current in Inductor and Capacitor with DC voltage source? [closed]

A DC source in series with pure Inductor and pure Capacitor no Resistance. How the current will flow in this circuit? What I just know is that in the beginning Inductor will behave as an open circuit ...
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1answer
184 views

Why isn't energy stored in a capacitor equal to just $QV$ when it is fully charged? [duplicate]

I just learned that the energy stored in a capacitor is electrostatic potential energy. Also potential energy is a state function and is independent of the path. So, when the capacitor is fully ...
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1answer
51 views

Negative Electric Capacitance

I know electric capacitance is always positive (otherwise it doesn't make any physical sense). But the capacitance is related to the potential difference, which can be positive or negative, depends ...
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31 views

Scale-covariant decomposition of capacitance

I'm wondering if there is any good insight of how to evaluate a given capacitive geometry in such a way that it would be expressed as a function that depends only on two components: as a geometric ...
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1answer
93 views

is it possible to use capacitors to quickly charge batteries? [closed]

the charging cycle of batteries is very slow compared to capacitors. Is it possible to use capacitors to quickly charge and discharge them to slow charge the batteries? For instance the range anxiety ...
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3answers
158 views

Is capacitance calculated over a finite volume or over all space?

Is the capacitance of a system of conductors calculated in a finite volume or over all space? My question is motivated by the following problem. A volume $V$ in vacuum is bounded by a surface $S$ ...
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1answer
89 views

Where extra stored energy of Capacitor go ? [duplicate]

Suppose We have a capacitor with capacitance $\ C $ and charge $\ Q $ . So total stored energy is $$ E=\frac{Q^2}{2C} $$ Now if I connect a capacitor with same capacitance parallel with it then ...
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1answer
57 views

How does differing surface resistance in a parallel plate capacitor effect the field strength?

I have been trying to find out how using different conductive materials for each parallel plate for a parallel plate capacitor will effect the field strength. Meaning if one of the parallel plates ...
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2answers
124 views

Battery charging a Capacitor

Ok I know there is a similar question already on here, but mine takes it just a step further. What I would really love to know is exactly how much energy is being transferred from a battery into a ...
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4answers
243 views

How to calculate the work of the electrostatic forces in a parallel-plate capacitor?

The expression of the energy stored in a parallel-plate capacitor is: $$U = \frac{e_0\cdot A \cdot V^2}{2d}$$ with $e_0$ the vacuum permittivity, $A$ the surface of the capacitor, $V$ the applied ...
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68 views

Resistor and conductor and inductor

What I am gonna to have if: -an inductor is in parallel with a capacitor and all that group is in parallel with a resistor. I know that a capacitor in parallel with an inductor is: $$\frac{1}{Z}=\...
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46 views

Time constant for this RC circuit

Well one problem boiled down to the following RC ciruit- $C_1$ was initially charged with $q_o$ and I thought after closing switch connecting $C_1$ and $C_2$ the maximum current discharging will be $...
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21 views

What size aluminum foil capacitor would power an LED?

Inspired by this video where a $9 \mu F$ capacitor is made from aluminum foil, if I had students put this together in a classroom, one question I would have is what would it take to have this power an ...
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1answer
50 views

Breakdown field in a capacitor

Let us say that air breaks down at a field strength of $E_b$. For a capacitor to arc, does there need to be a path between the two conductors such that for every point on that path the electric field ...
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74 views

Capacitor and Pith Ball experiment

Suppose I first charge a capacitor so that one plate is positively charged and another negatively. Now I remove the charging source and ground only one of the terminals say negative terminal, will ...
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1answer
715 views

How does a bulb light up when it's connected in a circuit with an uncharged capacitor and a cell?

Since there is a capacitor, isn't it an incomplete circuit? How does the current flow across the dielectric medium? If a bulb was connected to a cell alone and if there was a break in the wires of the ...
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28 views

Comparison of capacitances

The figure shows two arbitarily shaped surfaces S1 and S2.S1 is a thin metal foil, which has been slowly beaten to form the surface S2 without any loss of charge.. S2 lies completely within or on the ...
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1answer
100 views

Electric field between capacitors [closed]

A parallel-plate capacitor consists of two parallel, conducting plates of area $A$, separated by a distance $d$. Each carries a charge of magnitude $Q$; positive on one, negative on the other. Using ...
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Why the magnitude, $E$, of the field vector is different for every sets of (parallel) plates?

This is quoted my textbook. I wonder why we can't reproduce the same magnitude on a different set of plates, if we make them the same size, same charge, and having the same electric potential, and ...
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1answer
108 views

Transfer function of an RC circuit

I'm trying to reach the transfer function of an RC circuit which I am told is $$\frac {V_R} {V_\text{in}} = \frac{R}{\sqrt{(R^2 + \frac {1}{\omega^2 C^2})}} \cos(\omega t - \theta) \, .$$ Is this ...