What is Capacitors: Definition and 881 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. .Scott

    Cement Capacitors based on carbon black and concrete for use in energy storage

    A recent article published in the Proceedings of the National Academy of Sciences (PNAS) describes a large electric capacitors based on carbon black and concrete. The device would be used for electric power storage - often in proximity to the electric power demand, for example, a home.
  2. PhysicsRock

    Why Capacitors in Parallels vs. Series: Coaxial Capacitor Case

    So my idea was to separate the capacitor into two individual ones, one of length ##l - a## filled with a vacuum and one of length ##a## filled with the glass tube. The capacitances then are $$ C_0 = \frac{2 \pi \varepsilon_0 (l-a)}{\displaystyle \ln\left( \frac{r_2}{r_1} \right)} $$ for the...
  3. V

    Potential difference between 2 points in a capacitor circuit

    In the given circuit, a transient current will flow and when this current finally stops at equilibrium, the charges ##q_1## and ##q_2## are assumed to deposit at the capacitor plates as shown below. The dashed line indicates an isolated system that will have it's total charge conserved. If I...
  4. 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...
  5. C

    Ranking charge stored on three capacitors by a battery

    For this problem, The solution is, I have a few questions about parts of the solutions, - Part(b): (1) Why do they assume that the capacitors are initially uncharged? Do they even need to make that assumption because it seems clear to me that we are finding the charge stored by each...
  6. C

    Finding possible combinations of capacitors given circuit capacitance

    For this problem, The solution is, Is the only way of finding the possible combinations is by drawing out circuit diagrams? Many thanks!
  7. Shreya

    2 Capacitors and energy density

    I developed three arguments to answer this question. Argument no 2 seems to be wrong, but I cant figure out why. I know one/more of my arguments are flawed. Please be kind to help me figure this out. Argument 1) Since they have same charge on them, the ##E## between them must be same. The one...
  8. M

    How do I incorporate electric fields into capacitors?

    I know that I’m supposed to use proportional reasoning, but where does electric field even fit in? For whatever equation, I know I’m supposed to see how increasing the voltage by either 2 and 4 volts related to electric field. If electric field is the same as “U”, then wouldn’t it be...
  9. S

    B Phase Difference of Current & Voltage: Capacitors, Inductors & Complex Numbers

    how does capacitors and inductors cause phase difference between current and voltage? how does complex number come into play to explain the relation between phase of current and voltage?
  10. J

    Lorentz Force In Capacitors

    I am searching online for resources regarding studies done on the effect of the Lorentz force due to short circuit faults in capacitors. Although a DC-link capacitor only sees the ripple, there would be high current during a fault. Since F=(qE + JxB), I am curious what the effects of the high...
  11. J

    I Proof of Q=CV for arbitrarily shaped capacitors

    What is a proof of the formula Q=CV for a capacitor with arbitrary but unchanging shape where C is a constant?
  12. A

    Engineering Voltage in capacitors within an Energy Harvester

    Hello! Consider this circuit; Now this is what happens with the circuit; i)At time t0, switch S1 is closed and the capacitor has its maximum capacity at this time C = Cmax ii)At time t1 the switch is opened iii)Due to the mechanical vibration, the electrodes are drained from the capacitor...
  13. R

    I Electrostatic Influence and Series-Connected Capacitors

    As you know, "in the classics" the charges of the capacitor plates are equal in absolute value and opposite in sign. However, let us consider a series connection of capacitors. In this case, a charge of the opposite sign is induced on every second plate of each capacitor due to electrostatic...
  14. nmfowlkes

    Potential Difference over Capacitors in Series

    V1 = Q/30 In parallel: C = C1 + C2 V2 = Q/(60 + 90) V1/V2 = 3 V1 = 3V2
  15. Shreya

    Design a combination of Capacitors

    My attempt was this: The textbook answer was: Is my approach wrong?
  16. V

    Capacitors in parallel or series

    To me it seems like the formula applies to capacitors of any shape or size, since textbooks never mention any limitations on capacitor type when stating these formulae.
  17. J

    Electronics Will this electronic circuit work? (back-to-back polar capacitors)

    All I need is for someone to look at my schematic and tell me if this circuit will work. Thanks.
  18. U

    Electrical circuit problem (resistors, capacitors, inductors )

    I did try redrawing the circuit at steady state , but I'm not really sure. I have attached the circuit that I tried drawing, I assumed the branch with the capacitors to be absent at steady state since current won't flow through them anyway. With this diagram I get the correct answer for Q 19 ...
  19. V

    Connecting two charged capacitors in series

    I looked at the solution of this problem since its a solved problem. I am having doubts with the charges relationship as is mentioned in screenshot below. The charges ##{q_3}^{'}## and ##{q_4}^{'}## are the charges after a a state of balance is reached. Why would the charges have the...
  20. V

    Uncharged capacitors connected in series

    I came across the following explanation from the famous book of Sears and Zemansky which I am unable to understand. I can get the initial part where a positive charge goes to the top plate of C1 since the point a is at a +ve potential causing free electrons to transfer from top plate of C1 to...
  21. P

    Do charges always lie on the inner surface of capacitors?

    Parallel plates A, B are 5mm apart, with charges +1C and -1C respectively. Parallel plates C, D are 2mm apart, with charges +1C and -1C respectively. Capacitor CD is slid between capacitor AB. Find the potential difference between AB. The key idea to solving this problem is to suppose that +1C...
  22. P

    Electrical energy stored by charged concentric spherical shells

    I thought up of this problem myself, so I do not have solutions. I would appreciate if you could correct my approach to solving this problem. Firstly, the charge induced on the inner surface of shell B is -q, and so the charge on the outer surface of shell B is Q+q. The energy stored can be...
  23. P

    Principle of superposition for charges/induced charges

    The key observation to solve the above problem is that the charge Q can be dragged out into a flat capacitor plate parallel to the 2 existing plates. Apparently, while the charge distribution on the 2 existing plates changes, the total charge induced on each plate remains the same, due to the...
  24. P

    Meaning of F = -dU/dx for capacitors

    I have noticed that F = -dU/dx in gravitation gives the attractive force experienced by both bodies. For capacitors, does F = -dU/dx give the force experienced by each capacitor?
  25. P

    Force needed to hold together a capacitor

    I have 2 methods, which give 2 different solutions: Let sigma = charge per unit area Let plate 1 be the left plate, plate 2 = right plate. Method 1: Because they are insulating, consider the electric field at 3 regions; region 1 to the left of plate 1, region 2 between the plates, and region 3...
  26. G

    Question about electrolytic capacitors

    How many days can I store unused electrolytic capacitors without electrical voltage but that this electrolytic capacitor does not present problems due to non-use and depolarization?
  27. 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...
  28. C

    Equivalent Capacitance of a Triangular Network of Capacitors

    Hi, I'm struggling with this question. I feel like I don't even know where to begin. It seems to be a relatively simple calculation, but would the effective capacitance between A and C not just be 1 microFarad? Obviously that can't be the correct answer because such a simple observation wouldn't...
  29. Ntip

    Designing Balancing Resistors for Series Capacitors: Factors Affecting IR

    I am lookin designing balancing resistors for series capacitors and understand that I need to consider the leakage current from the capacitors. I am trying to determine factors that would case the insulation resistance to decrease over time so I can design around that.
  30. greg_rack

    Charges of capacitors in series and in parallel

    Very simply, I can't understand why the charges of capacitors placed in series are all the same, and why even the total one(of the circuit) is equal to those. How is it possible that the total charge is the same as the individual ones? There must be some concept/property about capacitors which...
  31. greg_rack

    Final electric potential difference in a circuit with two capacitors

    So, each capacitor must have a different potential difference, given by its capacity and charge... this would cause charge and current accordingly to flow in the circuit. But how do I determine the final potential difference, which would of course be the same for both of them? I have tried...
  32. B

    Redistribution of Pre-Charged Capacitors

    I first calculated the charge each capacitor has after its directly charged by the 36 V battery. ##Q_1 = C_1 * V = (2 \mu F) * 36 V = 72 \mu C## ##Q_2 = C_2 * V = (5 \mu F) * 36 V = 180 \mu C## ##Q_3 = C_3 * V = (7 \mu F) * 36 V = 252 \mu C## Then these capacitors connect in series, so I...
  33. Kaushik

    Question about charged capacitors and inserting a dielectric into one

    First when it is connected to the battery, the capacitors start accumulating charges such that the potential difference equals that of the battery. Then the current stops flowing. ##Q_1 = CV## ##Q_2 = nCV## Where 1 and 2 represent the capacitor with capacitance C and nC respectively Then, when...
  34. Adesh

    Capacitors connected in series: Why is the voltage the same?

    Here is a circuit diagram: . We have three capacitors, with capacitances ##C_1##, ##C_2## and ##C_3##. Plates are labelled as ##A_1, A_2, A_3 ... A_6##. Point P is connected to the positive terminal of the battery and point N is connected to the negative terminal of the...
  35. Zeymare

    Electrostatics and capacitors

    i didnt understand anything really, i read it a few times but i don't get it
  36. G

    Understanding Capacitor Equations and Time Constants

    Well i don't you to solve the question for me but I want you to clarify the concepts pertaining to this question. My question is how do I write a equation for the circuit since the there is same charge on one of the capacitors. While writing the equation should i put the voltage across the...
  37. A

    Negative potential energy and capacitors

    https://www.mytutor.co.uk/answers/11559/A-Level/Physics/What-is-gravitational-potential-energy-Why-is-it-negative/ But a parallel plate capacitor is oppositely charged, so the plates attract. With the same logic don't they store negative energy and wouldn't you get the wrong answer from a...
  38. G

    A confusing question on capacitors and voltages across them

    In my opinion, the voltage across the C1 should be 9V as the potential on the side of the positive plate of the capacitor should be (15-6)V and on the other be 0V. Similarly the potential across C2 should be (7-0)V. Here I'm basically assuming that the voltage at the negative terminals of the...
  39. 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...
  40. G

    Finding the potential across capacitors in capacitor-only circuits

    I tried to attempt it by applying KVL to both the loops. I tried to find a possible charge distribution for the capacitors. I guess this is right. On solving I get: from what I know potential difference between M and N is Q1/C2 but the solution is given as: Where am I wrong?
  41. J

    The voltages across capacitors in series

    I found total capacitance and inserted the total capacitance and emf of cell in equation CV =Q. However I know that there is a resistor connected so that this accounts for lost volts
  42. core1985

    If I connect two 4700 uf capacitors in parallel with my 8.3A battery

    Dear Friends Read my post carefully. I have a motor bike having 8.3A battery bike had 35Watt headlight which was pretty bad. I decided to connect car beam 100w/130w as my battery total power is 12 x 8.3 = 99.6 Watt so you know it can only provide 90% power to 100w point only. Now tell me...
  43. J

    'A' Level question on capacitors

    I have been looking at this question:-Now, I have found the charge in the whole system to be 36.0nC. I did this by 'condensing' the two 2.0nF into a single 4.0nF one, that then leaving me with an equivalent system of a 4.0nF capacitor & a 6.0nF one? I then found the equivalent capacitance of...
  44. V

    Can High Activation Energy Explain the Rapid Discharge of Capacitors?

    I would be grateful if someone could explain where my reasoning or assumptions are wrong.
  45. N

    Are capacitors the superior alternative to lithium ion batteries?

    I'm an undergrad physics student, so, I don't yet know much about the technicalities behind using chemical batteries vs capacitors. However, from what I've learned so far, capacitors seem to be a far better option than lithium ion batteries - they're not hazardous (at least when discharged), do...
  46. M

    Prove to me how capacitors in parallel can have the same V across plates

    *If at any point I say something incorrect or its clear I don't have the right understanding of something, please point it out and correct me. I need to be sure I'm understanding it all correctly. So please don't answer unless you're willing to read this entire post* So I know capacitors in...
  47. Romain Nzebele

    Capacitors in Series: 0.00125 & 0.002 Coulombs

    I have no problems with part a). I used the formula for capacitance and determined the charges to be 0.00125 coulombs and 0.002 coulombs. The solution in the book is the same. For part b) my initial thought was that the charges will redistribute themselves so that each capacitor get the same...
  48. jisbon

    Potential difference in Capacitors

    Firstly, I'm given this complicated circuit as shown below. What I have to do first, is to simplify it, which I will need help in checking. One question here: It's not possible to simplify this by adding resistors in series and capacitors in series am I, right? Or is it possible in this case...
  49. jisbon

    Capacitors (charging after long time)

    Hi there, So as far as I know, after long time, current doesn't flow through the resistor That means the voltage drop across the capacitor is equal to the EMF of the cell = 9V So will the charge be ##U = 0.5CV^2## = ##0.5(10)(81)##? Answer appears to be wrong, not sure what I am doing wrong here.