The ability of an object to store electric charge.

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58 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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39 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 ...
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1answer
109 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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74 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
157 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 ...
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37 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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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 ...
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106 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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304 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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77 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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35 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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79 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
245 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
91 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
42 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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0answers
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
64 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
149 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
63 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
34 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
97 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
174 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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56 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: ...
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35 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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17 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
42 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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58 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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311 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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27 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 ...
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1answer
69 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. ...
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18 views

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
84 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 ...
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2answers
272 views

How long does it take for a capacitor to be fully charged if voltage is decreased? [closed]

Above is the picture of the circuit pertaining to this question. The question asked for the time it will take for the capacitor to get fully charged when the switch is in position B? So i guess the ...
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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 ...
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34 views

Capacitor Plates should get charged even if one plate is connected to charge source

I have a two capacitor plates separated by a distance. I have connected one of the plates(call it plate A) to positive terminal of battery and and other plate( call it plate B) to negative terminal of ...
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2answers
186 views

Current on both sides of a capacitor

When a capacitor is connected to a DC circuit, what ensures that the current on both sides of the capacitor is the same? When charges arrive at one end of the capacitor they stop moving; presumably ...
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1answer
259 views

Work done by battery and potential energy of a capacitor

I have a doubt about the work done by a battery and the potential energy of a capacitor? 1- Consider a circuit where the capacitors are connected to the terminals of a battery. Through calculations ...
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1answer
108 views

Grounding a capacitor

When one of the plates of an isolated capacitor is grounded, does the charge become zero on that plate or just the charge on the outer surface become zero?
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28 views

Where can I find a good theoretical treatment of conductor shielding?

Suppose one has three current carrying cylinders lying on the same plane. Some of the electric field of the first conductor ends up on the second conductor, which creates capacitance C12. But also ...
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32 views

What is the capacity of this circuit? [duplicate]

I simply can't figure out what the capacity of this circuit is. I can do the math myself, I just need a hint how to create an equivalent circuit where it is obvious what is parallel and what is in ...
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1answer
116 views

How is the formula for the capacitance of a parallel plate capacitor derived?

I have seen in I.E. Irodov that if the permittivity is given as $\epsilon$ then we can find the capacitance as $$C = \frac{\epsilon A}{d}$$ but I wonder whether it is dimensionally correct or not and ...
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44 views

Coaxial waveguide - wave impedance

Determine the capacity $C$ per $m$, the inductance $L$ per m and the wave impedance $Z_0$ for a coaxial waveguide with inner radius $a$ and outer radius $b$. How large would $b$ have to be so ...
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1answer
137 views

Cylindrical capacitor in an electric circuit

I've come across a tricky question and would appreciate some hints or explanations as to why the given solution is the way it is. The question reads as follows: A coaxial cable consists of a wire ...
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2answers
117 views

Charge between parallel plates given voltage

When you connect a parallel-plates capacitor to a voltage source, why is it assumed that the plates will have equal but opposite charge? According to the formula, the voltage only fixes the charge ...
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19 views

Total current - differential equation [duplicate]

Consider the circuit below consisting out of a capacitor C and two identical resistors R. For $t<0$ the switch is open and the capacitor is uncharged. At $t=0$ switch is shut and the circuit is ...
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1answer
231 views

Circuit with capacitor and two resistors - total current - charge - differential equation [closed]

Consider the circuit below consisting out of a capacitor C and two identical resistors R. For $t<0$ the switch is open and the capacitor is uncharged. At $t=0$ switch is shut and the circuit is ...
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61 views

Maximum current in LC Circuits

Two capacitors of capacitance $C$ and $3C$ are charged to potential difference $V_o$ and $2V_o$ respectively and connected to an inductor, all three in series. Now the switch S is closed. Find the ...
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1answer
239 views

Loss in energy while charging a capacitor

Suppose a capacitor having capacitance $C$ is being charged using a cell of emf $E$. By the time the capacitor is fully charged, the cell has supplied $QV$ energy while the potential energy of the ...
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1answer
222 views

Capacitance of three plates

I'm sorry if this has been asked before, but here it goes. Consider three parallel plane conducting plates (they can be infinite) and suppose the middle plate has some thickness $\delta$ and the other ...
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1answer
179 views

Why is this electric field due to one plate of a capacitor $\sigma / 2 \epsilon_0$ when the capacitor plates are finite?

We know that electric field due to an INFINTE large sheet is constant and at INFINTY the electric field is not zero. But say if I take a finite sheet of length l and width w. Then the electric field ...