The ability of an object to store electric charge.

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Distorted colors of Google StreetView photographs near electric power lines

This is a followup to my question: Cyclist's electrical tingling under power lines Some users presented a convincing picture that the electric shocks under power lines are primarily from the ...
15
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2answers
418 views

Are there analogs to resistance, inductance, capacitance, and memristance connecting the weak force to electromagnetism?

A question was asked over at EE.SE recently which I tried to answer, but much of my answer was speculative. I'm hoping someone here can help my ignorance. In electronics design, there are four ...
13
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3answers
3k views

Is there a deep reason why springs combine like capacitors?

I was solving a practice Physics GRE and there was a question about springs connected in series and parallel. I was too lazy to derive the way the spring constants add in each case. But I knew how ...
12
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5answers
808 views

Where's the energy in a boosted capacitor?

Suppose I look at a parallel plate capacitor in its rest frame and calculate the electrostatic energy, $E$. Next, I look at the same capacitor in a primed frame boosted in the direction perpendicular ...
11
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5answers
44k views

What is the difference between a battery and a charged capacitor?

What is the difference between a battery and a charged capacitor? I can see lot of similarities between capacitor and battery. In both these charges are separated and When not connected in a circuit ...
11
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8answers
33k views

Why does the voltage increase when capacitor plates are separated?

In lab, my TA charged a large circular parallel plate capacitor to some voltage. She then disconnected the power supply and used a electrometer to read the voltage (about 10V). She then pulled the ...
11
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4answers
988 views

Capacitance of two almost-touching hemispheres

This capacitor is composed of two half spherical shelled conductors both with radius $r$. There is a very small space between the two parts seeing to that no charge will exchange between them. So ...
9
votes
2answers
997 views

Are capacitors and inductors mirror images of each other?

I'm reading through my E&M textbook (Physics for Scientists and Engineers 3rd edition, Knight) and watching as many lectures on YouTube (Shankar, Pomerantz, Lewin, etc) to prepare for next ...
9
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3answers
2k views

Why do charges enter the capacitor in the first place?

I have been studying Capacitors for the past year now and the one thing I don't understand is how a charge is stored on the capacitor. Essentially, a circuit with a capacitor is an incomplete circuit ...
8
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4answers
3k views

A problem of missing energy when charging a second capacitor

A capacitor is charged. It is then connected to an identical uncharged capacitor using superconducting wires. Each capacitor has 1/2 the charge as the original, so 1/4 the energy - so we only have 1/2 ...
7
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2answers
1k views

Capacitance of Non-concentric Spheres

We all know how to obtain the capacitance $C=\frac{ab}{b-a}$ (ignoring constants) for two concentric spheres of radii $a,b$. I was just thinking to myself, what would happen to the capacitance for ...
7
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4answers
6k views

Will a charged capacitor discharge if one lead is connected to ground?

If I charge a capacitor and connect one lead to ground keeping the other lead floating, will the capacitor discharge ? ...
7
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1answer
276 views

What does a relativistically moving capacitor “look” like? [duplicate]

Suppose I have a parallel plate capacitor with a vacuum between the plates, a voltage $V$ across them and a capacitance of $C$. What will this arrangement look like to an observer in a uniformly ...
6
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4answers
2k views

What is the current of a capacitor when the derivative of voltage is undefined?

This is from the textbook I am reading: I know this equation for capacitors: $$i=C\cdot \frac { dv }{ dt }$$ Here is my question: how can diagram (a) be allowed if the derivative of the voltage ...
6
votes
2answers
195 views

What stops charges from jumping across a capacitor?

I've learnt in class that charges store up on capacitor plates (the electrons). But why don't the electrons just jump across capacitor, what stops them? At first I thought perhaps it might just be the ...
5
votes
1answer
11k views

What defines the maximum charge a capacitor can store?

The formula for a capacitor discharging is $Q=Q_0e^{-\frac{t}{RC}}$ Where $Q_0$ is the maximum charge. But what property defines the maximum charge a capacitor can store? If it depends on ...
5
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3answers
3k views

Capacitor with different charges on each plate

I am confused as to whether/how capacitance changes when each plate has a different charge. For example, consider a coaxial cable and put $20Q$ on the outer cable, and $-Q$ on the inner. Or how about ...
5
votes
2answers
41k views

What is the electric field in a parallel plate capacitor?

When we find the electric field between the plates of a parallel plate capacitor we assume that the electric field from both plates is $${\bf E}=\frac{\sigma}{2\epsilon_0}\hat{n.}$$ The factor of two ...
5
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4answers
665 views

Energy Gain with capacitor?

I have a question about energy gain in capacitors. Assume the following system: As the electron gets accelerated inside the capacitor, it will have more kinetic energy coming out than going in. But ...
5
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2answers
13k views

Capacitor circuits with light bulb

Let's say we have a normal circuit with a light bulb, with wires and a battery. When one places a capacitor in this circuit, how is the light bulb able to light up, even when the capacitor prevents ...
5
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2answers
2k views

Why does a capacitor discharge?

Suppose a charged capacitor (parallel plates), the negative and positive charges on two plates attract each other. Which force cause the negative charge carriers (electrons) move through the circuit ...
5
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2answers
12k views

What happens to capacitor’s charge when the plates are moved further apart?

In my physics textbook there is an example of using capacitor switches in computer keyboard: Pressing the key pushes two capacitor plates closer together, increasing their capacitance. A larger ...
5
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3answers
2k views

What's the difference between Capacitors, Ultra-Capacitors and Batteries

Capacitors are known to hold and release energy very quickly, unlike the slower release that batteries exhibit. If one were to bunch many (1000's of) capacitors together could they function as a ...
5
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3answers
3k views

Charge Distribution on a Parallel Plate Capacitor

If a parallel plate capacitor is formed by placing two infinite grounded conducting sheets, one at potential $V_1$ and another at $V_2$, a distance $d$ away from each other, then the charge on either ...
4
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3answers
694 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 ...
4
votes
4answers
7k views

If we charge a capacitor can we discharge it into a battery?

I have read that we can charge a capacitor using a battery, but can the vice versa happen? My project needs to show a battery being charged through a fully charged capacitor.
4
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3answers
654 views

Change in attraction of charged bodies

If I insert a piece of glass between two objects carrying different charges, would they still attract? If they attract, does the piece of glass affect the force of attraction and is there any formula ...
4
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3answers
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How feasible is it to use the dielectric constant of a liquid to determine specific gravity?

I homebrew my own beer and I'm looking for way to cheaply monitor the specific gravity of my brew during the fermentation process. I came across this thread that seems to indicate capacitance may be ...
4
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2answers
2k views

Charge distribution on a plate of Capacitor with Dielectrics .

I had this Homework Problem with a capacitor (parallel plate) that has a group of 3 dielectrics between it like so : Now We were asked to find the equivalent capacitance and the distance of ...
4
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2answers
551 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 ...
4
votes
2answers
830 views

Equivalent RC circuit to a RRC circuit?

I'm in doubt about a situation that I've seen sometimes: imagine we have a resistor in parallel with a resistor and a capacitor in series. Since I don't know how to generate figures of circuits to ...
4
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1answer
2k views

How would I explain a farad being a second per ohm?

The farad has many alternative representations in SI. I can comprehend some of them. For example, a capacitance of 1 farad means that it will take a single coulomb to create a single volt between the ...
4
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3answers
5k views

Electric field intensity in a dielectric inside a capacitor

In the question A parallel plate capacitor is charged from a cell and then isolated from it. A dielectric slab of dielectric constant $K$ is now introduced in the left half region between the ...
4
votes
1answer
99 views

How to get a function for the voltage across a capacitor connected to an AC voltage source? [closed]

I am looking for the way of obtaining a solution for $V_{c}$ ,as a function of $t$ depending of $\omega$, of the following differential equation related to an electrical circuit involving a low-pass ...
4
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1answer
2k views

What do physical properties of materials trigger the capacitive touch screen?

I have watched some youtube videos about capacitive touch screen http://www.youtube.com/watch?v=ZHzaVzYEZbw http://www.youtube.com/watch?v=GmCE18RMEeQ The videos show that a conductor(finger), in ...
4
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3answers
1k views

How can I find the potential created by spherical capacitor with dielectric material?

If we have a spherical capacitor with inner radius or r1 and outer radius of r2, with charges (+/-)q on them and there is a dielectric material (with constant e) in between them with. What kind of a ...
4
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1answer
51 views

Mutual capacitance upper limit

I am having trouble making an analog for mutual capacitance from mutual inductance. In circuits with magnetic coupling, there is an upper limit established on mutual inductance due to energy ...
3
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4answers
1k views

Does a capacitor ever get fully charged?

The time $t$ taken by a capacitor of capacitance $C$ in a charging circuit with a resistance $R$ in series with it to accumulate charge $q$ is given by the equation $$t = \tau ...
3
votes
2answers
95 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 ...
3
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5answers
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Capacitors and Resistors - Series or Parallel?

I recently came across a problem in which a 12v DC power supply is connected in parallel to (in one loop) a one microfarad capacitor and a one kilo-ohm resistor. In the other loop is a 1000 microfarad ...
3
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2answers
290 views

What is zero impedance in AC circuit?

If a capacitor is connected with an inductor, then because $$Z=\frac{1}{j\omega C}+j\omega L,$$ the Z may be zero. Does that mean when I apply a voltage, the current will be infinite large? What's ...
3
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4answers
8k views

Electric field outside a capacitor

I know that the electric field outside of a capacitor is 0 and I know it is easy to calculate using Gauss's law. We create cylindrical envelope that holds the same amount of charges (of opposite ...
3
votes
4answers
3k views

Is a capacitor in an open circuit charged?

Say I have a circuit consisting of a battery, a wire, an open switch, and a capacitor. The circuit is open since the switch is open. My book says that the capacitor will only be charged when the ...
3
votes
2answers
2k views

Capacitors in series: Why is the equivalent charge the same as the individual charges

Consider two parallel-plate capacitors $C_1, C_2$ in series. For the "equivalent" circuit, clearly $$ Q_{equiv} = C_{equiv}V$$ should hold, where V is the total voltage drop between input and ...
3
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1answer
284 views

Electric field and capacitance across a resistor

Using a simple lattice model of conduction, where electrons are accelerated by an electric field, and are slowed down by bumping into the lattice, you get the following equation for current density: ...
3
votes
1answer
208 views

Capacitance of two cocentric spheres, contradicting results

Suppose we are given two conducting, cocentric spheres of radius $a_1$ and $a_2$ respectively. The inner sphere with charge $q$, the outer sphere with charge $-q$. I can calculate the capacitance of ...
3
votes
2answers
283 views

Moving the plates of a charged capacitor to calculate energy density - where's the flaw in my argument?

For a charged air-dielectric capacitor, let the plates be parallel to the $xy$ plane, with the top carrying a positive charge $+Q$, the bottom a charge $-Q$. The force on an infinitesimal charge ...
3
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1answer
403 views

Capacitance of a conducting disk

I'm reading this(PDF) derivation of the capacitance of a thin conducting disk. The surface charge density of such a disk can be shown to be: $\sigma(r) = \frac{Q}{4\pi a\sqrt{a^2 - r^2}}$ (in ...
3
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1answer
4k views

What is the role of battery across a Parallel plate capacitor having equal charge?

Each plate of a parallel plate capacitor has a charge $q$ on it. The capacitor is now connected to a battery. Now, which of the following options are correct? a) The facing surfaces of the ...