Questions tagged [capacitance]

The ability of an object to store electric charge.

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1answer
27 views

Current in RC circuit using Thevenin's equivalents or Kirchoff's laws

Say we have a DC circuit with multiple capacitors and resistors (and batteries) in it. All capacitors are assumed to be initially uncharged. Suppose we're interested in finding the current through ...
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1answer
23 views

Adjustment Required for Force between Plates of a Parallel Plate Capacitor

The parallel plate Capacitor is not an Infinite sized charged sheet system. But in Most derivations of Force between the Charged plates due to the electric field and charges between/on the plates is ...
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Self-capacitance of electrodes in capacitors

I thought about a way in which we could increase self-capacitance of electrodes in a dielectric capacitors. Is it possible to create an internal electric field in each electrode which would have an ...
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1answer
41 views

Question about capacitance on a double cylinder [closed]

I had an exercise that I am struggling to solve, I have 2 concentric metal surfaces with $R_1= 1 \,\text{cm}$ and $R_2 = 2 \,\text{cm}$. The cylinders have infinite extension along the direction ...
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4answers
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Force between the plates of a capacitor

As we know that the electric field between two parallel plates of a capacitor is $$E=\frac{\sigma}{\epsilon_0}$$, so the magnitude of force exerted by one plate on the other should have been $$F=QE$$. ...
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2answers
325 views

Why can we consider two conducting spheres very far apart from each other as a capacitor?

If we have two conducting spheres of equal but opposite charge and they are at a large distance from each other, why can we consider this system as a capacitor? According to my textbook, this is valid....
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74 views

Discharge only one plate of capacitor?

what would happen if : Charge a parallel plate capacitor with battery Then disconnect the battery And finally, connect the positively charged plate to battery ground (similar to the induction-charged ...
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3answers
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Failing to understand use of one-dimensional upper limit in area variable

I am trying to learn capacitance of a parallel plate capacitor, while learning i noticed the portion where they are calculating potential using line integral. Now, there is a term "ds" which is the ...
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1answer
31 views

Law of conservation of energy and circuits

How does the law of conservation of energy work in circuits? If we have a voltage source to which a resistor, capacitor and and an inductor are connected, then will the kinetic energy of the ...
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1answer
247 views

Why does total charge stay the same when capacitors are connected in parallel?

A capacitor of unspecified capacitance $C_1$ so that the potential difference across it is $84.0\ \mathrm V$. It is then disconnected from the voltage source and connected in parallel with a $12\ \...
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1answer
39 views

Effective time constant of an RC circuit

I have read in some books that to determine the equivalent time constant of charging of a capacitor in any RC circuit containing either only one capacitor and any number of resistors arranged in any ...
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2answers
78 views

Why is a resistor always connected to a capacitor in series? [closed]

In my physics lecture I was told that one must always connect a resistor to a capacitor in series, because it allows it to charge quicker and the time constant becomes smaller. Why does this happen? ...
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1answer
97 views

In a fixed voltage case, why does inserting a dielectric increase the energy by a factor of $K$?

When inserting a dielectric, the electric field will do a positive work, and it will lose energy to attract the dielectric. by comparison, when dielectric is inserted in a charge-constant case, this ...
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28 views

Is there such a capacitive transformer?

I've been thinking if it's possible to have voltage transforming effect based on capacitor. Will it work if a ferrite core, those "I" and "E" plates, be placed, and istolated throught mica, between 2 ...
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3answers
72 views

Why does the dielectric field not cancel out the capacitor's field?

When a conductor is in a region with electric field, free charges will move until they balance out the external electric field. However in dielectrics this does not happen. I know that charges are ...
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1answer
129 views

Proof that elastance matrix is invertible

I was reading this lecture notes from MIT OCW on capacitance . It says $V_i =\sum_j P_{ij}Q_{j} $ where the constants $P_{ij}$ are determined by the geometry of the conductors. This matrix can ...
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1answer
33 views

Inductor real charcaterstics when connected to an ac supply

When we connect a dc source to an inductor we always use a resistor there so after solving that RL D.C. circuit we find an exponential function (e to the power R/L based) But when we are considering A....
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1answer
160 views

Is a radio receiver antenna a capacitor?

I think so, but its capacitance should be very small, so how can the antenna correctly receive the signal, the low capacitance wont bother the signal?
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3answers
978 views

Field inside a plate capacitor with a dielectric material

Suppose I have two plate electodes with a dielectric material between them with a permitivity of $\epsilon=10$. I now put a voltage V between them. What is the electric field in the dielectric region? ...
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1answer
210 views

Why is aluminium foil wrapped around a Leyden jar?

In the process of constructing a water Leyden jar, a foil of aluminium had to wrapped around the outside of the Leyden jar. What purpose does it fulfill?
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2answers
26 views

Which part of circuit becomes electron deficient during charging of an RC circuit?

During the charging of an RC circuit via a battery charge gets accumulated in the capacitor. But according to the conservation of electric charge, some part of the circuit must become electron ...
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25 views

Resonant and non-resonant terms in $RLC$ cirquit

I have tried to solve a differentials equations of a RLC circuit. In the the solution I have terms proportional to $e^{iw_0t}$ and $e^{-iw_0t}$, where $w_0= \sqrt{1/LC}$. The author proposes in the ...
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5answers
417 views

Why complex numbers are used in electronics? [duplicate]

The impedance of a capacitor or an inductor is imaginary. How do we know these quantities are imaginary?
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35 views

Capacitance of partially filled coaxial cylinders [closed]

Consider a concentric system of (say metallic) cylinders as I have drawn in the picture. A solid/filled cylinder is embedded in the outer one. The red lines are the electrical contacts on the top and ...
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25 views

What is $C_\mathrm{eq}$ for this circuit? [duplicate]

What is $C_\mathrm{eq}$ for this circuit? I don't even know how to approach such a problem.
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4answers
125 views

Where does energy go in joining capacitors of different capacitance charged by different potential, hypothetically assuming no resistance in circuits?

I don't understand why there is any change in initial and final energy since we have already assumed a perfectly conductive circuit. I mean, theoretically at least, there should be no change in energy....
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19 views

How do I find the equivalent capacitance of this circuit? [duplicate]

I am trying to solve the given problem, which asks to find the equivalent capacitance for this circuit. Everything is given in the diagram. How would I go about solving this? I understand that at the ...
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1answer
215 views

Why does charge on a capacitor remain constant when dielectric is fully inserted between the plates of the capacitor?

We have a capacitor let's say of capacitance C and is charged by Voltage say V. Then the voltage is disconnected and a dielectric of dielectric constant say k is inserted fully between the plates of ...
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4answers
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Is there a physical explanation for why increasing a capacitor's capacitance and the circuit's resistance decrease the capacitor's rate of discharge?

The voltage across a capacitor as a function of time is given by: $$V=V_ie^{-t/RC}$$ Therefore, increasing the resistance and capacitance increases the time it takes for the initial voltage to drop ...
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1answer
153 views

AC pass through capacitor [closed]

I am confused how AC passes through a capacitor? Can any one explain or provide any video how AC passes through a capacitor?
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What material should I use for the plates of my homemade mica capacitors?

I recently acquired some mica as i want to build my own high voltage (50 kV if possible) capacitors. The problem I am encountering right now is that the surface of such a crystal isn't perfectly flat ...
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2answers
917 views

Why do the charges on a parallel plate capacitor lie only on the inner surface?

In most pictures I've seen of parallel plate capacitors, charges are drawn so that they're entirely on the inner surface of the plates. I accept that there can't be any net charge within the ...
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2answers
695 views

How does a Leyden Jar work?

When electricity goes inside the Leyden jar, the inside of the jar is negatively charged. Then the aluminum foil on the outer layer of the jar is positively charged. Does the inside of the jar want to ...
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0answers
17 views

Large Equivalent series resistance for polarized capacitor

Consider a standard RC circuit with a $100 k\Omega$ resistor and a capacitor. Here's some issue encountered during the lab. When using specifically a polarized capacitor($20 \mu F$), in addition of ...
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Ferroelectric energy storage

Let say we have a ferroelectric capacitor which is capable to store 1 joule of energy. Then we remove charged plates and remain only fully polarized ferroelectric. Are there some ferroelectrics which ...
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1answer
41 views

Energy stored in a capacitor vs Work that the battery does [duplicate]

Say we have a battery at a fixed voltage of $V$ charging a capacitor with capacitance $C$. When the capacitor is fully charged, the energy stored in it will be $\frac{1}{2}QV$, where $V$ is the final ...
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1answer
53 views

Why is the field inside a capacitor not the sum of the field produced by each plate?

In this answer by David Z, we can read, When discussing an ideal parallel-plate capacitor, $\sigma$ usually denotes the area charge density of the plate as a whole - that is, the total charge on the ...
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3answers
136 views

How do electrons flow when a capacitor is connected to a battery with certain voltage?

If there is an insulator between the conducting plates of a capacitor which is connected to a battery, the circuit is open. Since the pathway for electrons to flow is impeded by the insulator, how ...
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2answers
157 views

RC time constant in parallel circuit [closed]

$R_1 = 50k \Omega $ $ R_2 = 100k \Omega $ $ \mathcal{E} = 10V $ $ C = 10 \mu F $ So I want to find the $\tau$ time constant of this circuit after the switch is closed. The only issue is that ...
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1answer
28 views

Circuit breaker and capacitance

I have a problem with knowing witch capacitor to use in a circuit because I am working on installing main circuit breaker where it is needed for 220 Volt AC current to be turned in to a lower current ...
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4answers
2k views

Why is there no current between two capacitors connected in series?

I want to ask a question about the figure below. Why the current does not flow from $-Q$ term to $+Q$ term or from a to b since there is a voltage?
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2answers
34 views

Work done by an electric field in this case

Assume the following problem: Two parallel-plate capacitors with different distances between the plates are connected in parallel to a voltage source. A point positive charge is moved from a point 1 ...
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1answer
33 views

$E$-field between dielectric and plate in parallel plate capacitor and Feynman's claim

Feynman says about $E_{0}$ below Note that the field $E_{0}$ between the metal plate and the surface of the dielectric is higher than the field $E$; it corresponds to $\sigma _{free}$ alone. $\...
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1answer
18 views

Time constant relevance and definition for an RC or any 1st order RC/RL or a 2nd order RLC circuit

Can someone clearly explain what it is meant by the time constant of an RC circuit. Because from what I have been told it is the time taken to charge the capacitor. However, when I search on google it ...
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1answer
36 views

How do I find the charge on this capacitor in a complex circuit with multiple batteries? [closed]

! I have the answer to this question, it's 8*10^-6 C. But I have no idea how to get this answer.
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9answers
4k views

Inductor and Capacitor in Parallel

I've been staring at this for 10 minutes and I'm soooo confused. Hopefully, you guys can help! So, let's say we close the switch. From what I understand, the capacitor will charge up to $10V$ almost ...
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1answer
37 views

How do I derive the frequency of oscillation of the capacitor voltage? [closed]

The formula is $$\omega= \frac{1}{\sqrt{L \times C}}.$$ How do I derive this?
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2answers
56 views

Attenuation of a signal

Suppose that I have a wire between two terminals and I want to send a high frequency ($f$) signal from one to another. Is the inductance and capacitance per unit of distance enough to calculate the ...
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30 views

Cylindrical/Spherical Capacitor derivation sign issues

In deriving the capacitance for a cylindrical and spherical capacitors, I keep obtaining the incorrect sign on V. I completely understand the problem besides one step. First we start with Gauss' law:...

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