What is Capacitor: Definition and 1000 Discussions

A capacitor is a device that stores electrical energy in an electric field. It is a passive electronic component with two terminals.
The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator. This name and its cognates are still widely used in many languages, but rarely in English, one notable exception being condenser microphones, also called capacitor microphones.
The physical form and construction of practical capacitors vary widely and many types of capacitor are in common use. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, air, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, although real-life capacitors do dissipate a small amount (see Non-ideal behavior). When an electric potential (a voltage) is applied across the terminals of a capacitor, for example when a capacitor is connected across a battery, an electric field develops across the dielectric, causing a net positive charge to collect on one plate and net negative charge to collect on the other plate. No current actually flows through the dielectric. However, there is a flow of charge through the source circuit. If the condition is maintained sufficiently long, the current through the source circuit ceases. If a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor.
The earliest forms of capacitors were created in the 1740s, when European experimenters discovered that electric charge could be stored in water-filled glass jars that came to be known as Leyden jars. Today, capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in early digital computers, and still is in modern DRAM.

View More On Wikipedia.org
Recent contents Top users
  1. J

    Time for a capacitor to discharge

    I already how to properly set it up and execute the equation with natural log etc. 2/3q0 = q0e^(t/RC) 2/3 = e^(-t/tau) ln(2/3) = -t/tau t = -ln(2/3)tauThe problem should be trivial; however, -ln(2/3)tau is apparently incorrect. So is ln(3/2). Is there something I am missing?
  2. Ntip

    Capacitor type selection for power converter

    I am looking at capacitor selection for a switched capacitor converter and I'm not sure which voltage rating to look for. I've was going to consider the DC rating since they're holding off a DC voltage, but they are subject to PWM excitation since they're switching between nodes at different...
  3. PhysicsTest

    Problem related to a parallel plate capacitor

    The diagram would look like this. a. The total energy is conserved, ##KE_A + PE_A = KE_B + PE_B ## ##KE_A=0; PE_A =1000## ## 1000 = \frac{m v^2} {2} ## ##2000 = {9.1}*10^{-31}*v^2## ##v^2 = \frac{2000 * 10^{31}} {9.1}; v = 46.8 * 10^{15} ## ##v = at; = \frac {qVt} {md} ; t = \frac{vmd} {qV}...
  4. P

    Dielectrics inside a parallel plate capacitor

    Could somebody check my solution?
  5. lekh2003

    Electrical How to use capacitors in a Solenoid circuit

    I've been working on designing an experiment over the past few weeks as part of a school project, under the supervision of a teacher. I have designed a small low-power coil-gun. I have a coil of roughly 60m 24 AWG copper wire wrapped around a length of 2.5cm of clear PVC pipe. I tested the...
  6. wcjy

    Effect of Leakage on Capacitor Energy Storage

    $$R_{eff} = R_1 + \frac{1}{\frac{1}{R_2}+\frac{1}{R_3}} = 1.4 + 0.6 = 2$$ PD of R3 = 4 / 2 * 0.6 = 1.2 Net PD of the capacitor = 2- 1.2 = 0.8V $$ E = \frac {1}{2} CV^2$$ E = 0.8 ^2 * ( 3*10^-6) / 2 E = 9.6 * 10^-7 Correct answer is: 4.27 * 10^-7 was thinking if i should find the Effective...
  7. G

    Sizing the start capacitor for an induction motor

    A friend has a single phase, cap start induction motor with the following characteristics: V 240/250 A 2.6 Hp 1/3 Rpm 1435 @ 50Hz As for as I know it’s not fitted to a machine, but given the low hp rating I’d guess it’s for a drill press. So it would need only moderate to low starting torque...
  8. P

    Parallel Plate Capacitor with Dielectric Connected to a Battery

    Not sure how to set this question up or how to get to the second half
  9. madafo3435

    Find the capacitance of a half-full capacitor

    The capacitance must be found, that is: ##C=\frac {Q}{V_a-V_b}##. Let ##\vec{E_d}## and ##\vec{E_v}## be the electric fields due to the zone with dielectric and the zone without dielectric respectively. In the case of a spherical capacitor with a vacuum between its plates, it is easy to...
  10. greg_rack

    Discharge of a capacitor and current in an RC circuit

    I'm having a few troubles understanding a few things about this circuit... Firstly, what does "In light of this, the potential between the resistors is ##16V##" exactly mean? If current isn't flowing, how could there be a potential between resistors? Secondly, how does current flow with the...
  11. A

    A capacitor of variable capacitance

    Using: $$i(t)=\frac{U}{R}.e^{-\frac{t}{RC}} As the power is constant, then the current will be constant, so: t/RC is constant I don't know how to proceed anymore. I think you should use some derivative, but I'm still very new to that part, so how can I proceed?
  12. P

    A Parallel plate capacitor in the Rindler metric

    Does anyone have a reference or solution for a parallel plate capacitor in the Rindler metric? I'm particularly interested in the case where the capacitor plates are in the xz or yz planes, z being the direction of the acceleration. The motivation is to get an idea how a transmission line...
  13. archaic

    Current leakage between the charged plates of a capacitor

    1)$$\frac{Q}{\Delta V}=\frac{\kappa\epsilon_0A}{\ell}\Leftrightarrow\Delta V=\frac{Q\ell}{\kappa\epsilon_0A}$$$$I=\frac{A\Delta V}{\ell\rho}=\frac{Q}{\kappa\epsilon_0\rho}$$ 2) The charge is decreasing by ##\Delta Q##, so ##Q(t)=Q-\Delta Q##.$$I=\frac{\Delta Q}{\Delta t}\Leftrightarrow\Delta...
  14. archaic

    Inserting a dielectric between the plates of a parallel plate capacitor

    a)$$C=\frac{\kappa\epsilon_0\ell x}{d}+\frac{\epsilon_0\ell(\ell-x)}{d}=\frac{\epsilon _0ℓ\left(\kappa x+ℓ-x\right)}{d}$$ b)$$U=\frac{1}{2C}Q^2=\frac{dQ^2}{2\epsilon _0ℓ\left(\kappa x+l-x\right)}$$ c)$$F=-\frac{dU}{dx}=\frac{dQ^2\left(\kappa -1\right)}{2\epsilon _0ℓ\left(\kappa...
  15. R

    A Capacitor With A Dielectric But Also Free Space in Between

    Lets go through the example problem until we get to the part I don't understand. Figure 25-17 can be used as a reference to all questions. From part (a) to part (b) we eventually find the charge q on one plate (and by default the charge -q on the other). No problem there. The battery is then...
  16. Kaguro

    Inserting a charged plate into a capacitor

    Potential depends on the charge contained by the conducting plate. So the plate C should change the electric field and hence potential on both plates A and B. This should change the absolute value of potential,but since A and B are still connected to that cell, I think the potential difference...
  17. G

    Tilting the plates of a parallel plate capacitor (and other changes)

    (a) (b) have intuitive solution but the asymmetry in (c) is confusing.
  18. K

    Griffiths 8.5: Impulse and Momentum parallel plate capacitor

    Summary:: Griffiths problem 8.5 Problem 8.5 of Griffiths (in attachment) I already solved part (a), and found the momentum in the fields to be $$\textbf{p}=Ad\mu_0 \sigma^2 v \hat{\textbf{y}}$$ In part (b), I am asked to find the total impulse imparted on the plates if the top plate starts...
  19. E

    Force on a capacitor plate as the derivative of the energy -- is it a fluke?

    Bit of a random question... capacitors can be a bit weird, in that if we connect one up to a source of EMF and do positive external work to separate the plates of the capacitor, the energy of the capacitor decreases (and instead the work you do plus the decrease in capacitor energy goes into the...
  20. Frigus

    How to simplify this capacitor circuit?

    I tried to find logic behind how do we simplified the circuit as given for 2 hours and I unable to find any clue. I can do it just by following rules but I am unable to get intuition. I tried to make sense of it but how can we even make two points as one.
  21. Tony Hau

    Relationship between radial distance and charge density of a capacitor

    So this is a question from my lab report on capacitance. The aim of the experiment is to find out the relationship between surface charge density and radial distance from the centre of the plate capacitor. And in this experiment I have recorded 5 sets of data, namely r=0, V=4, r=1, V=3.5, r=2...
  22. F

    If a mosquito zapper works as a capacitor

    If so how does the electric field around look like?
  23. F

    What happens to the capacitor and dielectric when an old phone charges faster?

    Is there any diagram showing the inner workings of the capacitor of a phone? If an old phone becomes less chargeable (takes less time to be fully charged), what happens to its capacitor and the dielectric?
  24. Nomadyb

    Find EMF of ℰ on Wire: Speed v, Force, C, B, m, g, l & a

    a) the EMF of ℰ induced on The Wire, as a function of the speed 𝑣of the wire you can find it. b) flow induced in the wire𝑖, 𝐶, 𝐵, and are denominated in 𝑙 𝑎 (𝑎= the acceleration of the wire). c) find the magnetic force acting on the wire in𝐶,𝐵, 𝑙 and𝑎. d) 𝑎 acceleration, 𝑚, 𝑔, 𝑙, and are...
  25. Fabio97

    Magnetic field for a capacitor

    .
  26. A

    Parallel Plate Capacitor Filled with Many dielectrics

    This is the problem I'm working on. So far I know: 1. I am assuming the free charge density is +sigma for the top plate and -sigma for the bottom plate. 2. The electric field from the plates goes from top to bottom plate, in the negative z direction. 3. The electric field of the capacitors...
  27. F

    The real reason for a capacitor having the same amounts of + and - charges on the two plates

    Most textbooks say that a capacitor whether it be a single one or one in series/parallel should have equal amounts of + and – charges on both plates and that they mostly conclude the + charges attract the same amount of – charges on the other plate without giving any reason. Now I claim that...
  28. qwereqe

    Detecting the Alignment of an Inf. Plane Capacitor: A Paradox?

    Assuming we have an infinite plane capacitor,where the upper plate is charged positively and the bottom layer is charged negatively. Now we know the field outside the capacitor is zero so we can't tell if the positive charge is on the upper plate or the lower plate. But, if we place it inside...
  29. G

    Capacitance of a spherical capacitor

    When I try to do Gauss, the permeability is not always that of the free space, but it varies: up to a certain radius it is that of the void and then it is the relative one. How can I relate them? I'm trying to calculate the capacity of a spherical capacitor. The scheme looks like this: inside I...
  30. B

    Charged capacitor connected to an uncharged capacitor

    Hi there, tried doing this question but not sure if what I did for part b is right? Appreciate any help! Thanks
  31. r-swald

    Find how far a proton travels between capacitor plates

    I first attempted to use kinematics, but to find acceleration I would need to find the force either by finding the e-field first and multiplying it with q, or just kQq / r^2. However, I was not given second charge or surface charge density. Is there another way I could go about making the...
  32. Kaushik

    Equivalent Capacitance Between X and Y in this capacitor circuit

    This is the problem. If someone asks you this question, how would you solve it? I am finding it really tough to solve when the circuit gets a bit complex. It would be nice if you share what exactly you'll do to solve complex circuits such as this (the algorithm).
  33. A

    AC motor rotary capacitor soft start

    I was wondering about , have there been or are there any systems that would use a large capacitance rotary capacitor/s as a mechanism for soft start of larger AC motors and also they would serve as power factor correction devices? The idea is basically simple, say one has a 3 phase motor and we...
  34. E

    Gauss' law for a physical capacitor with finite thickness plates

    In derivations of capacitance it is standard to consider two oppositely charged, infinitely thin sheets. If we construct a Gaussian cylinder across one sheet, we obtain ##E_{1} = \frac{\sigma}{2\epsilon_{0}}## for one sheet, and then we can superpose this field with that from the other at an...
  35. Mircro

    Material between capacitor plates - viewed as two capacitors in series

    This is a second grade high school problem, translated from my native language. I don't have a problem with calculating, but with understanding the concept. There is an instruction with the assignment that says: The capacitor can be viewed as a combination of two capacitors in series with...
  36. E

    Proving time constant formulas of a capacitor using Kirchoff's laws

    the attached files are a diagram of the circuit. also I believe I figured out how to proof equation (7) but I'm lost on how to proof (8)
  37. L

    How does this capacitor circuit not violate conservation of charge?

    There must be something I'm not understanding about capacitors in series. I know that we can treat them as one equivalent capacitor with: (1) with 1/Ceq, (2) same Q as anyone of the capacitors, (3) and add up the Vs for the sum total V across them. If the equivalent capacitor (Ceq) would...
  38. Praveen1901

    Kirchoff's laws and capacitance

    Equivalent capacitance before and after remains the same. Now the 10F capacitor (which was initially connected in parallel with 20F) would have 30 C charge. Hence an additional 20C must have been supplied to it. The only path which may supply the charge is through battery. However this leads...
  39. Prabs3257

    Heat dissipated in a Resistor-Capacitor circuit

    I tried to conserve the charge on the left plates of both the capacitors as intially the total charge on both is 48 and at t=t0 the total charge is 36(on c1) +4V(V is the potential across c2) so i got V=3 and then i conserved the energy Initial energy on both capacitor = final energy on both +...
  40. F

    B field between the plates of a charging capacitor (Ampere's law)

    A standard example consider a capacitor whose parallel plates have a circular shape, of radius R, so that the system has a cylindrical symmetry. The magnetic field at a given distance r from the common axis of the plates is calculated via Ampere's law: \oint_\gamma {\mathbf B} \cdot d{\mathbf...
  41. C

    Engineering Calculating the size of a capacitor in a sample and hold circuit

    First, I calculate the jitter power with an equation given in the book Next, I calculate the signal power Now, I know that SNR = Psignal/(Pjitter + PthermalNoise), However, I seem to be getting a negative value for the thermal noise power?? My plan was to use this thermal noise power and...
  42. K

    Discharging this capacitor in an RC bridge circuit

    The voltage source in the circuit below has been switched on for a long time when the switch S switches off. How long will it take before the current coming out of the capacitor has become less than 1 mA? My attempt: I am far from sure that my solution is correct. This is because i...
  43. C

    Engineering Charge Redistribution in a Capacitor Bank/DAC

    I have a question relating DAC architectures. The guts of the question are really to do with capacitors and charge. I want to see if my understanding is correct. This is not a homework question or anything, just thinking about how the circuit interacts. Setup: Consider the following setup...
  44. eyespy

    A circuit with switches, capacitators and resistors

    To solve this question first I calculated the potential energy the capacitor A stored. It's equal a: Ca.V²/2. Ok, so when switch S1 is open and S2 is closed I calculated the equivalent capacitance as if they were in series --> 1/Ceq = 1/Ca + 1/Cb --> Ceq = (Ca.Cb)/(Ca+Cb). So I used the formula...
  45. F

    Relay and Capacitor circuit - blinking LED

    Hello Forum, I am having issue understanding what is going on with the circuit below which is supposed to blink an LED by alternatively pulling the switch up and down which results in opening and closing the circuit the LED is part of (lower circuit portion). This is what I am confused about...
  46. H

    Electric field between two capacitor plates (proof)

    See attached image
  47. E

    Super Capacitor Series Circuit

    I'll make a power bank with capacitors and I made circuit of it. But I'm worrying about whether the circuit is safe, because it's dangerous to use capacitor. So, can you check the circuit i made?? My capacitor is 2.7V, 600F and the power bank circuit has "Charging current : 1A maximum, output...
  48. johnboyman

    Trying to calculate the peak current of a Capacitor bank

    Hello I am building a Tesla Coil. I built it well I attached an image of the circuit I used. I bought a 15,000 volt transformer rated at 30 ma. I think it is too small for my tesla coil because it keeps blowing a fuses and a red light turns on. Here are the specs. -Inductance (L): 17 uH...
  49. Charlie Cheap

    Using a capacitor for RFI protection

    It has been decades since I was in electronics school and I forgot a lot. I was told using copper plug wires could hurt modern electronic ignition parts, and I was wondering if an RFI capacitor (.5 mfd.) would help protect things. I have a 4-cylinder with points that have been changed to a...
  50. patrykh18

    Stress tensor for a parallel plate capacitor

    The question is partially taken from Griffith's book. I am confused about the physical meaning of momentum in fields. I have determined the solution and found that in part d the momentum crossing the x-y plane is some value in the positive z direction. I don't however understand the physical...
Back
Top