What is Capacitor plates: Definition and 49 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.

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  1. V

    Polarities of capacitor plates in a complex circuit

    (a) I think the top plate of C5 could end up with either + or - charge, and not necessarily + charge as shown. This is because the connected plates of C1, C5 and C3 form an isolated system to which we can apply the law of conservation of charge i.e. Total charge just before transient currents...
  2. 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...
  3. 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...
  4. maxipoblete

    Capacitance of a circular capacitor with two parallel dielectrics

    Hello, the problem is better illustrated at the picture below. The capacitor is isolated, with an initial charge Q0. I understand that Q0 does not distribute along the plates homogeneously. How could it be solved with the equivalent parallel circuit?
  5. L

    Work done when Inserting a Dielectric between Capacitor Plates

    Hi, today in lecture, we discussed the work done on inserting a dielectric between a capacitor. Two cases of this example: One case, where the battery is disconnected so that the charge stays constant. Other case where the battery stays connected so voltage is constant. I am confused on...
  6. Abhimessi10

    Charge entering into the field between capacitor plates

    Homework Statement A negative charge of mass m enters into the field between two deflecting parallel plates with length 'l' separated by distance 'd' with a velocity 'v'.Assuming electric field to be uniform,find the maximum charge so that it will not hit a plate Homework Equations Kinematic...
  7. H

    Electrostatic energy after a metal piece is inserted between 2 capacitor plates

    Homework Statement fig 1 : Area of each plate is S, separated by 2d, charge Q in the capacitors fig 2 : uncharged conductors of area S, thickness d, inserted parallel between plates What is the ratio of electrostatic energy in fig 2 to electrostatic energy in fig 1? Homework Equations Q =...
  8. P

    Charge density of capacitor plates

    Homework Statement A parallel plate capacitor is made of two flat horizontal conducting plates in a vacuum, each of area A, separated by a small gap. One plate carries a total charge 2Q, the other a total charge −Q. Find the surface charge densities on the four horizontal metal surfaces in...
  9. D

    Potential Energy and Force Between Capacitor Plates

    Hello guys, came across some Analytical Physics lectures (http://www.physics.rutgers.edu/ugrad/227_f11/classes/lect08.pdf) that got me confused. It is described in the lecture the problem of determining the force between capacitor plates for a constant voltage (ie. connected to a battery). For...
  10. P

    Force between capacitor plates

    What will happen to the force between the capacitor plates (Will increase or decrease or remain constant) if we introduce a dielectric between them? As per the answer given the physics textbook , the force will remain same? But as per my understanding the force should decrease since electrical...
  11. P

    Is Work Required to Move Capacitor Plates Apart?

    If I have a capacitor and I maintain the potential difference between the two plates as I move them apart would I have to do any work (other than mechanical work) to move them apart? my logic tells be I shouldn't have to as I'm not doing any work again the potential field? Just wondered what you...
  12. X

    Can electrons "fly" between capacitor plates?

    How exactly do the electrons move from the capacitor to the rest of the circuit? Do they fly between the capacitors plates, or can they only travel where there is a wire connection? (I.e., if a small chunk of our circuit looks like this: A-------| |-------B can an electron start from A, go to...
  13. Hijaz Aslam

    Charge induced on capacitor plates

    Homework Statement Three conducting capacitor plates are kept horizontally, above each other with a gap 'd'. If a charge ##+1\mu C## is kept on the middle plate what is the charge on the plates? Homework Equations (This question is theoretical) The Attempt at a Solution My textbook gave the...
  14. F

    Effect of capacitor plates at different angle

    Hi, I am interested to simulate the capacitor with plates having an angle of 195 degrees between them. https://dl.dropboxusercontent.com/u/32847378/cp1.jpg I know that if the angle between of plates is 180 deg, then electric lines of forces will follow a elliptical path and equipotential...
  15. AdityaDev

    What happens to charge stored in a capacitor when moving the plates?

    Let us take a charged capacitor and move the plates such that it the distance between them be constant. For example, one moves towards left and other moves upwards. Assuming only overlapping area affects capacitance... WILL THE CHARGE STORED IN CAPACITOR CHANGE? I know the capacitance changes.
  16. Feodalherren

    Changing the distance between capacitor plates

    Homework Statement 1. The distance between two parallel plates is increased while they remain hooked to a battery. Which one of the following statements is true? The voltage between the plates will decrease. The electric field between the plates will increase. The charge on the...
  17. Conservation

    Three Dimensional Charge Density in Capacitor Plates

    Hello everyone, I was wondering how one would calculate the three-dimensional charge density (per volume) in a capacitor plate with a given thickness. I know how to calculate the charge density on the surface based on the capacitance and voltage, but how would one calculate the comprehensive...
  18. C

    Charge on capacitor plates when separated

    As I understand it if you charge two plates as in a capacitor and then disconnect the voltage source and pull the plates apart to an arbitrary distance the voltage at the terminal increases. Is that correct? Will that voltage continue to increase? Is there a point that the voltage will stop...
  19. U

    What is the Velocity of the Capacitor Plates in an RC Circuit?

    Homework Statement In the following RC circuit, the capacitor is in the steady state. The initial separation of the capacitor plates is x0. If at t = 0, the separation between the plates starts changing so that a constant current flows through R. Find the velocity of the moving plates as a...
  20. F

    Force between capacitor plates at constant voltage

    I have a slight issue with this derivation. Firstly, displacing one plate by dx requires work dW=-Fdx where F is the internal force between the plates resolved in the direction of x. I.e F=-dW/dx. If I do work on the capacitor W, this plus the energy provided by the battery to keep the...
  21. Saitama

    Capacitor Plate Charges After Switch is Closed

    Homework Statement Plates of a capacitor have charge 2CE and CE initially. Now the switch S is closed. Which of following statements is true? Assume that the battery, resistor and wires do not have any capacitance. A)There is no change in charge at outer surfaces of the capacitor. B)There...
  22. P

    Calculate charge on object suspended between capacitor plates

    Homework Statement It would be greatly appreciated if someone could check over my work. It is very likely that I made mistakes. If I made any mistakes, could you please tell me where I went wrong? Thank you. I will use this problem to study for my next exam. I have also attached a...
  23. A

    Calculating induced charges by a charge between two capacitor plates.

    A charge Q is kept at a distance x from one of the plates of a parallel capacitor having plates d distance apart with cross section area A.The whole system is earthed.Find the value of induced charges on both the plates. I tried putting the sum of induced charges equal to Q and balancing...
  24. Saitama

    A fly between capacitor plates

    Homework Statement (see attachment)Homework Equations The Attempt at a Solution I don't understand the question. There are equipotential lines everywhere in the region between the capacitor plates, even at ##r_0## from the left plate. So the fly could simply fly along that line and the answer...
  25. T

    Work to Move parallel capacitor Plates

    Hi, in my book there are two capacitor plates distance x apart (they are kept connected to a constant voltage source). These plates are moved apart to distance 3x. In order to find the work done to move the capacitors apart (using W=F dl=QE dl), my book takes the charge Q of one plate and...
  26. M

    Relationship: Force on a charge at some distance from capacitor Plates

    Homework Statement Two capacitor plates (infinite plane) with uniform charge distribution but different charges (one positive, one negative) are distance "d" apart. A charge is place at d/2 and feels force |F1|. A charge is placed at d/4 and feels force |F2|. How does |F1| compare to |F2|...
  27. S

    What is the voltage across the capacitor plates?

    A 15μF capacitor is connected to a 55V battery and becomes fully charged. The battery is removed and the circuit is left open. A slab of dielectric material is inserted to completely fill the space between the plates. It has a dielectric constant of 4.8. What is the voltage across the capacitor...
  28. D

    2 op amp followers on 2 capacitor plates not measuing correct voltage

    I am currently trying to measure an 80pF capacitor using 2 voltage follower op amps. I have them both powered by a set of 2 1.25V rechargable batteries. They are op amp type LMP7721 link: http://www.ti.com/product/lmp7721 . Each op amp is configured such that the voltage out terminal [end...
  29. M

    Strangely aligned capacitor plates

    Working along step-by-step with a text and I'm stumped as to how they reached a conclusion. In the first picture you see two plates aligned at an unspecified angle, theta. One plate is at a potential V and the other is grounded. The distance between the plates at one end is d, and at the other...
  30. C

    Finding potential difference across capacitor plates?

    Homework Statement Two capacitors are identical, except that one is empty and the other is filled with a dielectric (k=3.6). The empty capacitor is connected to a -11V battery. What must be the potential difference across the plates of the capacitor filled with a dielectric so that it stores...
  31. C

    Electric Field Magnitude b/w Capacitor Plates

    Electric field magnitude between capacitor plates independent of distance? [SOLVED] The electric field of a point charge Q is defined as E=\frac{F}{q}=\frac{\frac{1}{4\pi \varepsilon _{0}}\frac{Qq}{r^{2}}}{q}=\frac{1}{4\pi \varepsilon _{0}}\frac{Q}{r^{2}} where q is the test charge. The...
  32. E

    Force between capacitor plates, partially filled with dielectric

    So for just vacuum in between one could say F=q*E = (σA)*(σ/2ε0) = A*σ^2 / (2ε0) Alternatively, F = dU/dx, where x is the separation. U = 1/2 CV^2 = 1/2 QV = x*A*σ^2 / (2ε0). To get V, we just add up pieces of E-field*distance. But now let's say part of x is a dielectric of thickness t...
  33. K

    An electromagnet made of a bunch of capacitor plates in series?

    Has anyone every tried to make an inductor made out of capacitors, that is to say, which uses the magnetic field of displacement current rather than that of electron current to generate magnetic fields? Let's say the gap between plates is greater than the thickness of each plate. Wouldn't most...
  34. T

    Is there a lower limit to the separation between capacitor plates?

    Let's say I build a parallel plate capacitor using two metal plates with perfectly smooth surfaces. They are separated by some small distance d, with only vacuum between them. I then apply some AC voltage across the plates. Is there some effect which causes loss in the capacitor (equivalent...
  35. B

    Separating capacitor plates: (+) or (-) work?

    Homework Statement Consider a parallel-plate capacitor with plates of area A and with separation d. Find F(V), the magnitude of the force each plate experiences due to the other plate as a function of V, the potential drop across the capacitor. Hint i used If the plate separation were changed...
  36. C

    Why is there a need to average the electric field between capacitor plates?

    As I have understood it, it is a classical problem to show that the force between to capacitorplates is \frac{1}{2}\epsilon _0 E^2 A, which is at first counterintuitive since one should think that it is QE = \epsilon_0 E^2 A. I am pondering that question a bit now and i saw the MIT lecture...
  37. A

    Force that holds capacitor plates

    For any capacitor, whose 2 plates or conductors are being held by a battery to a constant potential difference of V volts, there is a force of attraction between the plates, since they are oppositely charged. What is the force that 'holds' these conductors at their respective positions i.e. what...
  38. S

    Calculating charge outside capacitor plates

    Homework Statement A capacitor made of two parallel uniformly charged circular metal disks carries a charge +Q and -Q on the inner surfaces of the the plates and very small amounts of charge +q and -q on the outer surfaces of the plates. Each plate has a radius R and thickness t, and the gap...
  39. F

    Work required to move capacitor plates

    Homework Statement Determine the work required to move the plates of an ideal parallel plate capacitor from a separation distance of D to an integer multiple of D, (assume only one moves for simplicity). The each plate has an area A. Homework Equations F = q^2 /( 2 e_0 A) field strength...
  40. K

    Electric Field due to Capacitor Plates

    Homework Statement A capacitor consists of two plane parallel plates, separated by a distance d. The space in between is filled with a uniform charge density J. Find the electric field at a point x away from the positive plate when a potential difference V is applied. Homework Equations...
  41. J

    High frequencies and capacitor plates

    Hello, I was wondering at high frequencies, does current literally go through the capacitor plates; from one side to the other? Or is it simply due to charges being stored on the plates, that once the polarity of the circuit has changed, the charges on the plate that has been stored from...
  42. N

    Thickness of capacitor plates

    How does the thickness of the capacitor plates affect capacitance when the distance between the plates are comparable to the thickness of the individual plates?
  43. N

    Exploring the Relationship Between Parallel Capacitor Plates & Spheres

    This isn't a problem out of my book, just something I noticed while *doing* a problem on parallel capacitor plates. The problem gave me an area for each plate (1 m^2)and a desired capacitance (1 F)and prompted me to find the distance between the plates. C = q/v (capacitance = charge/potential...
  44. M

    Force Between Cylindrical Capacitor Plates

    Homework Statement Capacitor plates are length L with radii a,b a<b are co-axial and intially covering each other with line charge density of the inner plate Q/L. determine the force between plates as the inner plate is partially withdrawn along the axis. i) if cylinders charged to...
  45. B

    Outside the capacitor plates E is zero how potenital the same

    hi, We see theoretical discussion of Electric field inside the charged capacitor is confined in the space between the plates and E.d = potential difference between plates. Considering the battery terminal(let us say positive terminal), wire and left plate or top plate, being in the same...
  46. J

    Capacitor Plates: E Field Outside or Between Plates?

    Hello, Quick question. If you have a parallel plate capacitor charged with X volts. Is there a detectable E field outside the plates at all or only between the plates? Thanks, Jason O
  47. F

    What is the voltage across the capacitor plates

    Am I overthinking this problem? A 15uF capacitor is connected ot a 55V battery and becomes fully charged. The battery is removed and the circuit is left open. A slab of dielectric material is inserted to completely fill the space between the plates. It has a dielectric constant of 4.8...
  48. S

    Capacitor plates and tunneling current

    If two capacitor plates at a moderate voltage (200-300V) and low capacitance are kept very close to each other would there exist a tunneling current between them. If the tunneling current will exist, then it will gradually reduce the energy of the capacitor. Where will the used capacitor...