What is Capacitance: Definition and 899 Discussions

Capacitance is the ratio of the amount of electric charge stored on a conductor to a difference in electric potential. There are two closely related notions of capacitance: self capacitance and mutual capacitance. Any object that can be electrically charged exhibits self capacitance. In this case the electric potential difference is measured between the object and ground. A material with a large self capacitance holds more electric charge at a given potential difference than one with low capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the capacitor, one of the three elementary linear electronic components (along with resistors and inductors). In a typical capacitor, two conductors are used to separate electric charge, with one conductor being positively charged and the other negatively charged, but the system having a total charge of zero. The ratio in this case is the magnitude of the electric charge on either conductor and the potential difference is that measured between the two conductors.
The capacitance is a function only of the geometry of the design (e.g. area of the plates and the distance between them) and the permittivity of the dielectric material between the plates of the capacitor. For many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them.
The SI unit of capacitance is the farad (symbol: F), named after the English physicist Michael Faraday. A 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates. The reciprocal of capacitance is called elastance.

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  1. C

    Q: What is the Purpose of a Capacitance Bridge & How Does it Impact Output Q?

    What is the purpose of a capacitance bridge? let's say 4 capacitors are arranged ...../.|.\ .....c1..|..c2 ...____ /...0...\ _____ ...|...\...|.../...| ...|...c3..|..c4...| ...|...\..|../...| ...|......| ...|......| 0 indicates the voltmeter. if 0 indicates a potential of 0, we get...
  2. T

    Capacitance per length of co-axial cabel

    Find the capacitance per length of a co-axial cable with a conductor of radius a and a thin shield of radius b.
  3. C

    Time constant of photodiode? parallel stray capacitance?

    Hihi, http://sales.hamamatsu.com/assets/applications/SSD/si_pd_circuit_kspd1043e06.pdf 5. high-sensor From the message there, I don't understand what is the meaning of time constant of resistor? Why does it say that the time response of the circuit depends on the time constant...
  4. L

    How Do You Calculate the Charge and Energy in a Mixed Capacitor Circuit?

    1. Homework Statement a potential difference V = 100 V is applied across a capacitor arrangement with capacitances C1 = 11.0 µF, C2 = 7.00 µF, and C3 = 3.00 µF. Find the following values Charge on each capacitor, potential difference on each capacitor, and stored energy in Joules. The circuit...
  5. G

    Exploring Limiting Stray Capacitance with Fast Signals

    I was wondering, If we had a system in which we limited the stray capacitance by shortening the cable (standard co-ax) to about 1 foot, and we put a REALLY fast signal down there, say of the order of fs. Would we see a sharp spike which was of the order of the RC time constant (capacitance...
  6. W

    Capacitance Vs Frequency and Voltage

    Would you kindly help me in describing the relationship between 1. capacitance and voltage and why? and 2. Why does with increase in frequency the capacitance decreases ?
  7. C

    Capacitance Problem; somewhat solved, but units are off

    Homework Statement An air-filled spherical capacitor is constructed with inner and outer shell radii of 7.00 and 14.0 cm, respectively. (a) Calculate the capacitance of the device. (b) What potential difference between the spheres results in a charge of 4.00 microC on the capacitor...
  8. P

    How Do You Calculate the Charge on a Capacitor in Series?

    Homework Statement Three capacitors of capacitance 8, 9, and 5 μF respectively, are connected in series to a 4 V battery. What is the charge on the positive plate of the 9 μF capacitor? Homework Equations Q = C*E 1/C = 1/C1 + .. The Attempt at a Solution I drew out the circuit...
  9. C

    Finding Total Capacitance with Electrical Breakdown

    Homework Statement In figure 25-29, a potential difference of V = 100 V is applied across a capacitor arrangement with capacitances C1 = 13.0 µF, C2 = 6.76 µF, and C3 = 4.14 µF. If capacitor 3 undergoes electrical breakdown so that it becomes equivalent to conducting wire, what is the...
  10. S

    How Do You Calculate the Capacitance of Two Charged Parallel Plates?

    Homework Statement two parallel plates have equal and opposite charges of 0.01 coulombs. the electric field between the plates is 10^5 Newtons/coulomb and the separation between the plates is 2mm. what is the capacitance of the plates? Homework Equations capacitance C = Q/V where Q is charge...
  11. S

    Capacitance and electric potential

    Homework Statement a 100 pico Farad capacitor C_1 is charged to a potential difference of 50 volts. the charging battery is disconnected and the capacitor is then connected to a second uncharged capacitor C_2. if the potential across C_1 drops to 35 volts, what was the capacitance of C_2...
  12. S

    Capacitance of two different circular plates

    Does anyone know how to calculate the capacitance of two circular plates having different dimensions? Say the top capacitor plate has a diameter d1 and the bottom capacitor plate has a larger diameter d2 and air is in between the bottom and top plate. So, it is not a standard parallel plate...
  13. A

    Capacitance of parallet plate with dielectric spheres in between

    I want to calculate the capacitance of a system consisting a parallel plate and dielectric spheres of different radius and dielectric strength in between the plates. please give some mathematical derivation. I really need to know it,my career depends on it. Please help me. :) thanks &...
  14. Y

    Capacitors: Series Capacitance Concepts

    Homework Statement The sketch below is a side view of two capacitors consisting of parallel plates in air. The capacitor plates are equal in area but the plate separation differs as shown. Individual capacitors are specified with two letters, for example WX is a single capacitor. The charge on...
  15. S

    Capacitance of point charge electrode

    Consider a capacitor which is just like a plate capacitor, but instead of the upper electrode being a plate it is a point charge Q. the lower plate is held at a fixed potential V=0. how could you calculate the capacitance of the system? when trying to calculate - it looks like it will be 0...
  16. N

    Capacitance and electric fields

    [SOLVED] Capacitance and electric fields Homework Statement I want to find the capacitance of a parallel-plate capacitor consisting of two metal surfaces og area A held a distance d apart. First I find the electric field, which I know is \frac{\sigma }{{2\varepsilon }}. Then I use that the...
  17. S

    Calculating Capacitance and Electric Force in a System of Connected Capacitors

    I'm trying to figure out the capacitance of the attached system. may I look at this problem as N capacitors attached in a cascade connenction? I'm also trying to figure out the force that will be felt by the point charge. I thought about using the image method... could you thing of a...
  18. B

    Self Capacitance of Coils & Shielding: Calculate & Understand

    Hi, I am reading conflicting things about self Capacitance when Shielding a Coil, can someone help.. IE: I have a coil of wire --say 25 turns, 250mm dia formed from looping in my hands & bound together with a non conductive thread. I have read on some sites that there is no affect on...
  19. E

    Capacitance and Inductance of Thin Metal Ribbons

    Homework Statement 21. A certain transmission line is constructed from two thin metal “ribbons”, of width w, a very small distance w<<h apart. The current travels down one strip and back the other strip. In each case it spreads out uniformly over the surface of the ribbon. a) Find the...
  20. Y

    Capacitors: Series Capacitance Concepts

    Homework Statement The sketch below is a side view of two capacitors consisting of parallel plates in air. The capacitor plates are equal in area but the plate separation differs as shown. Individual capacitors are specified with two letters, for example YW is a single capacitor. The charge on...
  21. V

    Capacitance of parallel plates as a function of distance

    Capacitance= (permitivity x Area of overlap)/ distance between two plates Why is capacitance inversely proportional to the distance between two plates? I understand that C=Q/V. So capacitance is the amount of charge it takes to change the potential difference between the two plates by 1...
  22. E

    Engineering Capacitance for a parallel RC circuit

    Homework Statement A circuit consists of a Zener diode, capacitor and resistor in parallel. Voltage to be maintained across the components is 4.7V, power 5mW. Find the values for resistor and capacitor Homework Equations (Below) The Attempt at a Solution I found the resistance by...
  23. D

    Engineering Circuit, capacitance, resonance

    Hi all; So the problem goes as follows: For the circuit in the figure, what should be the capacitance C to put the circuit into resonance? What is then the RMS value of the current? What is, then, the peak value of the air-gap flux density? Is, then, the assumption about infinite...
  24. ~christina~

    Capacitance in Circuit: What is the Equivalent Capacitance and Energy Stored?

    Homework Statement Assume that C_1= 10.0 \mu F, C_2= 5.00\mu F, and C_3= 4.00\mu F. A potential difference of V= 100V is applied across this network of capacitors. 1st picture is original (after that is when I simplified the circuit or tried to anyhow) a) find the equivalent capacitance...
  25. S

    Calculating Capacitance in Parallel Plate Capacitor with Third Metal Plate

    1. There are two parallel plates with distance between them 10 mm. Square of each plate is 100cm2. The third metal plate of thickness 8mm is situated in parallel inside the air gap. Find capacitance of this capacitor.
  26. Y

    Infinite Capacitance: Uses & Implications in JFET Circuits

    Theoretically only, would a capacitor of infinite capacitance be considered an open circuit? What would it be used for in application if it did exist? The reason I am asking is because I have a homework problem where it is used with a JFET transistor in a circuit. If I can't solve the...
  27. D

    Why Does Plate Separation Affect Capacitance?

    Hi, I'm doing a piece of (A-level) coursework into the factors that affect the capacitance of a parallel plate capacitor. After searching the internet I've come up with the following explanation for why plate separation affects capacitance: "Capacitance is inversely proportional to plate...
  28. C

    What is the capacitance of each capacitor?

    Two capacitors when connected in parallel give an equivalent capacitance of 9.00 pF and an equivalent capacitance of 1.55 pF when connected in series. What is the capacitance of each capacitor? in parallel: C1 + C2 = 9.00 pF in series: (1/C1) + (1/C2) = (1/1.55pF) My attempt: (C1 +...
  29. C

    Help with total capacitance in parallel and in series

    According to its design specification, the timer circuit delaying the closing of an elevator door is to have a capacitance of 33.0 µF between two points A and B. (a) When one circuit is being constructed, the inexpensive but durable capacitor installed between these two points is...
  30. I

    The capacitance of the two metal sphere system

    the capacitance of two metal sphere system Homework Statement What is the capacitance of the two metal sphere system. *The question has been attached shematically. All the variables are given in the attached file, there is no missing variable. thx for any help.
  31. G

    Charge Distribution Between Two Conducting Spheres

    [SOLVED] Capacitance and Charge 2 conducting spheres, one of diameter .400m and the other of diameter 1.00m, are separated by a distance large compared to the diameter. The spheres are connected by a wire and the system charged to a total of 7.00x10E-6C (total charge of system). How is the...
  32. S

    Capacitance and Max Potential Difference

    Homework Statement (a) Determine the capacitance of a Teflon-filled parallel-plate capacitor having a plate area of 1.90 cm2 and insulation thickness of 0.0600 mm. (b) Determine the maximum potential difference that can be applied to the capacitor. kV Homework Equations I THOUGHT C =...
  33. M

    Capacitance (should be simple)

    The problem. A 2.50uF capacitor is charged to 857V and a 6.80uF capacitor is charged to 652V. These capacitors are then disconnected from their batteries. Next the positive plates are connected to each other and the negative plates are connected to each other. What will be the potential...
  34. M

    Electric Feild and Capacitance

    Homework Statement A homemade capacitor is assembled by placing two 9inch pie pants 5cm apart and connecting them to the opposite terminals of a 9V battery. Estimate A) the capacitance, B) the charge on each plate c) the electric field halfway between the plates d) the work done by the battery...
  35. M

    Capacitance Homework Word Problem

    The problem. A 2.50uF capacitor is charged to 857V and a 6.80uF capacitor is charged to 652V. These capacitors are then disconnected from their batteries. Next the positive plates are connected to each other and the negative plates are connected to each other. What will be the potential...
  36. M

    What is the potential difference and charge on capacitors connected in series?

    I was hoping someone could help me approach this problem. A 2.50uF capacitor is charged to 857V and a 6.80uF capacitor is charged to 652V. These capacitors are then disconnected from their batteries. Next the positive plates are connected to each other and the negative plates are connected...
  37. T

    Capacitance in series and parallel circuit

    [SOLVED] Capacitance in series and parallel circuit Homework Statement Determine the equivalent capacitance between A and B for the group of capacitors in the drawing. Homework Equations Cseries = 1/Cs = 1/c1 + 1/c2 + ... Cparallel = Cp = C1 + C2 + ... The Attempt at a Solution...
  38. H

    Capacitance, Charges, Voltages

    Homework Statement Consider a charged parallel-plate capacitor. How can its capacitance be halved? Check all that apply. Double the charge. Double the plate area. *Double the plate separation. *Halve the charge. *Halve the plate area. Halve the plate separation...
  39. F

    Electric Potential, Work, and Capacitance

    Homework Statement A parallel-plate air capacitor has a capacitance of 920 pF. The charge on each plate is 2.60 µC. How much work is required to quadruple the separation?Homework Equations C = \frac{Q}{V} V = EdThe Attempt at a Solution In previous parts of the question, I was able to find...
  40. L

    Capacitance Help: Calculating Earth-Cloud System µC

    Homework Statement In lightning storms, the potential difference between the Earth and the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, and can have an area of 90 km^2. For the purposes of this problem...
  41. P

    Capacitance: (multiple choice)

    A capacitor is first connected to a 6.0 V battery and then disconnected and connected to a 12.0 V battery. How does the charge on one of its plates change: (a) It increases, (b) it decreases, or (c) it 1stays the same? (c) (because the charge on the plate is depending upon...
  42. A

    Equivalent capacitance; complex circuit

    [SOLVED] Equivalent capacitance; complex circuit Homework Statement Hello, I was assigned a problem where we are supposed to find the equivalent capacitance of a circuit, and then use that to answer some other questions. However, I'm not sure how to handle this circuit...
  43. H

    Capacitance vs. Distance of separation

    [SOLVED] Capacitance vs. Distance of separation Homework Statement Hi, I am suppose to make a capacitance vs (1/d) graph. I understand that the relationship between the capacitance and distance between the plates is inversely proportional and that it does not produce a straight line. My...
  44. A

    Calculating Capacitance for a Light-Bulb and Capacitor Circuit

    Homework Statement Imagine that you have a light-bulb that has a resistance of about 10 Ω and that can tolerate a maximum voltage of 3 V. Imagine that you want to connect this to a charged capacitor large enough to keep the bulb glowing reasonably brightly for more than 10s. Roughly what...
  45. R

    Capacitance of Axon: Calculate Farads

    Homework Statement An axon is the relatively long tail-like part of a neuron, or nerve cell. The outer surface of the axon membrane (dielectric constant = 5, thickness = 1 x 10^-8 m) is charged positively, and the inner portion is charged negatively. Thus, the membrane is a kind of...
  46. D

    How Does Fringing Field Capacitance Change with Conductor Shape and Size?

    Hi, I am having two doubts about the fringing field capacitance. 1) In most of the formulae, the fringing correction for the capacitance is written per unit length. This is ok if the length is very large; and the width and gap between the two conductors are only comparable. But is there...
  47. A

    How to measure parasitic capacitance between rf cable and metal surface

    dear all can anyone tell me.. if i have a transmission line passed above a metalic surface, there will be a parasitic capacitance between the line and the surface. and it induces interference how can i measure it. and if there is any refrenece about the allowable induce voltage...
  48. M

    Analogy Between Conductance & Capacitance

    Hi all... I want more information about the analogy between calculating the capacitance C and the conductance G ?
  49. S

    Load Capacitance of Oscillator

    What happens if I'm changing load capacitance of oscillator from 15pF to 30pF.
  50. K

    Factors influencing the varaiation of depletion capacitance of MOS capacitor

    Hi , i am interested to know physics behind MOS capacitors, on which iam currently working in . i started to fabriacate a MOS capacitor without using oxide (silicon dioxide) layer, i have read in articles that a MOS capacitor can be fabricated by using the native oxide layer ( naturally formed...
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