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.
1. Three equal capacitors, all with values C, are in series with a battery of V volts. If the middle capacitor is changed to 2C, what will be the resultant potential across each capicitor? Express your answer in terms of V.
Homework Equations
C = Q / V
The Attempt at a...
I have a question about coefficients of capacitance..
Specifically I'm reviewing the treatment on the subject in Chap 3.6 in Purcell's classic book on E&M. He starts out by considering a system of four conductors (actually 3 main conductors, and an "infinte" boundary condition surrounding...
Homework Statement
you have a 10 volt battery and two separate circuits with capacitors. One circuit has the capacitors in series, the other has the capacitors in parallel. Find the energy stored
one capacitor is 5.3 microfarads
the other capacitor is 2.4 microfarads
Homework Equations...
Im having trouble calculating the capacitance of a non-parallel plate capacitor where separation at one edge is d-a and the other it is d+a, assuming a<<d. I'm supposed to prove that C= epsilon_not A/d (1+a^2/3d^2). Thanks for the help.
Homework Statement
A spherical capacitor is made of two insulating spherical shells with different dielectric constants k1 and k2 situated between two spherical metallic shells and separated by a vacuum gap. Geometrical dimensions of the cross-section are as shown in figure 2. Calculate the...
A spherical capacitor is made of two insulating spherical shells with different dielectric strengths, k1 and k2, situated between two spherical metallic shells and separated by a vacuum gap. Calculate the capacitance of this system.
Total C = Q(free) / \DeltaV where \LambdaV is the...
Not sure where I was supposed to post this; but I think here it will hopefully get the attention of someone who can help me.
I am working on a project where I have to measure capacitance very accurately. I have been given a: ASL MODEL 1055 MANUAL DISPLACEMENT METER. But I've been, along with...
Hey gang,
I am doing a Mastering physics question, and it's got me stumped. ><
Q: You need a capacitance of 50.0 microF, but you don't happen to have a 50.0 microfarads capacitor. You do have a 80.0 microF capacitor.
What additional capacitor is needed to get a capacitance of 50 microF...
Homework Statement
This is for a lab I'm doing tomorrow. We will have a 10V circuit with 4 100µF capacitors connected in series. I need to calculate the voltage drop across each capacitor. I also need to create another circuit, but I'll worry about that after I'm sure I'm doing this one...
What is the capacitance of the sun? semms like a straigtforward question but I can't seem to find any information on what it is. I'm don't know if it has been measured, or if its even possible to measure, but I would have thought a body that big and active as the sun would have an ability to...
Each capacitor in the combination shown in the figure below (C = 11mF) has a breakdown voltage of 17.0 V. What is the breakdown voltage of the combination?
On either side of C is an equivalent capacitance of 40 mF (since these are parallel). I'm not certain where to go with this problem...
The figure below shows six concentric conducting spheres, A, B, C, D, E, and F having radii R, 2 R, 4 R, 6 R, 7 R, and 9 R, respectively. Spheres B and C are connected by a conducting wire, as are spheres D and E. Determine the equivalent capacitance of this system.
I understand that spheres...
Homework Statement
http://books.google.com/books?id=1DZz341Pp50C&pg=PA678&dq=serway+four+capacitors+are+connected&sig=iwUiJRqZDNHDGOfQfHHvh_9aQ3Y
problem 41 on this link. I got the equivalent capacitance for part a. for the two capacitors with 15 and 3uF- C_{eq}=2.5uF
for capacitor...
Homework Statement
A 6V DC voltage source is connected across both a 5kohm resistor and a 10 nF capacitor in series. The voltage drop across the resistor is what?
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Homework Equations
The Attempt at a Solution
should the charge=0 sicne by connecting wires across the...
capacitance a function of height...
the question I find difficult is:
A liquid-level transducer consists of two parallel plates of conductor immersed in an insulating liquid, as illustrated in this figure:
http://peecee.dk/?id=71007
When the tank is empty (i.e., x=0), the capacitance...
Hi,
As you know the capacitance per unit length of a standard coaxial cable is
C_{coax} = \frac{2 \pi \varepsilon_{0} \varepsilon_{r}}{\ln{\frac{b}{a}}}
where b is the radius of the cable and a is radius of the central conductor.
.
If we only want to know the capacitance of a...
Homework Statement
What is the equivalent capacitance for the following schematic?
Note that C1 is 11 µF, and C2 is 3 µF.
http://img511.imageshack.us/img511/8051/questionzi5.png
Homework Equations
C_{parallel} = C_1 + C_2 + C_3 + ... + C_n
\frac{1}{C_{series}} = \frac{1}{C_1} +...
Hello there
I'm currently working on an EM device that should be able to measure the humidity in the ground. I cannot give too many details, but let's consider the following issue:
I have a copper closed loop in which I send some current to generate a magnetic field. But there are some EM...
Homework Statement
http://img509.imageshack.us/img509/8805/problem5fw8.th.png
The potential difference V = 100 V is applied to the capacitor arrangement shown in the figure. Here C1 = 10 microF, C2 = 5 microF, and C3 = 4microF. If capacitor C3 undergoes electrical breakdown (i.e. becomes...
Three capacitors of capacitance 5, 7, and 2 mF respectively, are connected in series to a 1 V battery. What is the charge on the positive plate of the 7 mF capacitor?
so if the capacitors are all connected to the battery... than all of them have to have a electrial potential of 1 v
since...
Homework Statement
A small object of mass m carries charge q and is suspended by a thread between the vertical plates of a capacitor. The plate separation is d. If the thread makes an angle \theta with the vertical, what is the potential difference between the plates.
Homework Equations...
hi, all:
I am going to calculate the planar capacitance, of which one plane is in different position to anther. For example:
a)
******
.....***********
b)
*
*
*
*
...**************
c)
...*
...*
...*
..*
*
...*************
'*' represents the metal plane.
The...
Homework Statement
A parallel plate capacitor is constructed by placing square metal sheets of side length 30 cm on either side of a sheet of polythene which is 2mm thick
If the permeability of the polythene is 2.2 *10^-11 F m^-1, what is the capacitance of the system
(ii)If a 50V power...
I would like to calculate theoretically the capacitance of a bearing with metallic rings and ceramic spheres (see http://en.wikipedia.org/wiki/Rolling-element_bearing.
The expression for a cylindrical capacitor is: (2*pi*eps0*l)/(lnb/a).
However, when adding some spherical balls inside the...
Homework Statement
A known voltage source V_0 is connected by a switch to two capacitors in series with capacitance C_1 and C_2. When we flip the switch, connecting the capacitors to the voltage source, we measure the voltage across each capacitor, V_1 and V_2 respectively.
I need to...
Homework Statement
You're the operator of a 1.80×104 V rms, 60 Hz electrical substation. When you get to work one day, you see that the station is delivering 6.10 MW of power with a power factor of 0.850. How much series capacitance should you add to bring the power factor up to 1.0...
I have an assignment question with a variable capacitor in it and it asks what value of capacitance is necessary to provide "unity power factor overall". This wasnt explained in class, does anyone know what it means?
Homework Statement
In the diagram V = 12.0V, C1 = 23 uF, C2 = 4.00 uF, C3 = 12.0 uF and C4 = 9.00uF. Calculate the equivalent capacitance of the system.
http://img403.imageshack.us/img403/6346/eqam8.jpg
Homework Equations
Just combinding capacitors in parallel and in series...
I’m a bit confused on the relationships among C,V, and Q after reading my text. I don’t know if my reasonings contradict each other for the following.
Homework Statement
A capacitor of capacitance C holds a charge Q when the potential difference across the plates is V. If the charge Q on...
Homework Statement
To repair a power supply for a stereo amplifier, an electronics technician needs a 100 micro-F capacitor capable of withstanding a potential difference of 90V between its plates. The only available supply is a box of five 100 micro-F capacitors, each having a maximum voltage...
Homework Statement
http://img65.imageshack.us/img65/5993/clipboard01vk3.jpg
Homework Equations
Capacitance for series and parallel connected capacitors; C=Q/delta_V, derivations of last formulaThe Attempt at a Solution
Part A
C1 and C2 appear to be connected in series. Therefore, use...
1. 3 conducting spheres of radius a, b, c (a<b<c) are held at a potential of 0, V, 0 respectively. What is the capacitance of the system?
2. Q=CV (which I assume extends to Qi=CijVj for multiple conductors).
3. I've calculated the fields in the two interesting regions, calculated the charge on...
Homework Statement
The two plates of a parallel-plate capacitor initially carry equal amount of positive charge. If some charges are transferred from one plate to another, the charges on the plates are respectively +900uC and +100uC. The potential difference across the plates becomes 4V. What...
Homework Statement
Consider Earth and a cloud layer 700m above Earth to be the plates of a parallel-plate capacitor. If the cloud layer has an area of 1.9 km^2, what is the capacitance?
Homework Equations
Q = CV
V = Ed
E = Q/epsiolon*A
The Attempt at a Solution
Solving for C gives...
OOO|---C5----|
OOO|OOOOOOOOO|
A----C1---C2---C3----B
OOOOOOOO|OOOOOOOOOO|
OOOOOOOO|----C4----|
The "C"s stand for capacitor.
The capacitance of C2 is 10 μF and others are 4 μF.
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The book contains neither the answer nor solution.
I tried to apply Kirchhoff's Loop Rule...
Dear friends,
I am building a CDI system to ignite fuel mixtures in a pressure chamber for flame speed measurements.
I need a capacitor of about 5 nF, but it should hold up to 10 kV.
Any suggestions on where I can get those. I also need a diode (rectifier) for 10 kV. Also I need high...
Alright I have the answers... I was just hoping someone could explain how you would go about getting those answers
http://us.f13.yahoofs.com/bc/44436150me3e0859f/bc/My+Documents/Picture+1.png?bfwadIFBB1QyCb1K"
To Part A & B
I have learned how to find equivalent capacitence when capacitors are in series and when they are in parallel, but I came across a problem where I'm confused about the capacitors:
Normally I first find equivalent capacitence of parallel capacitors by adding them together. Then use the...
Hi,
Does anyone know an equation/approximation/model or other to estimate the capacitance between two coplanar (adjacent) plates?
I know that for parallel plates: C = E0*Er*(A/d). I also know that the capacitance decrease as the plates move from a parallel to a coplanar geometry as the...
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 10-8 m) is charged positively, and the inner portion is charged negatively. Thus, the membrane is a kind of capacitor. Assuming that an axon...
I've got a few more I need help with...I think I might have these ones, but not quite sure...as the concepts are still new to me.
1. If the voltage between the plates of a parallel plate capacitor is doubled, the capacitance of the capacitor...
A. is halved
B. remains the same
C...
have a question in regards to capacitors in series. We are taught that the charge must be equal on all plates of the capacitors in the case of a series connection. However, we also know that Q = CV. If we increase V, then Q must increase. How is this possible for the node between the two...
another for the EE pros out there
an isolated spherical capacitor has charge +Q on its inner conductor of radius r-sub-a and charge -Q on its outer conductor of radius r-sub-b. half of the volume between the two conductors is then filled with a liquid dielectric of constant K. a) find the...
Hello,
I've learned from my study of oscillator circuits that an inductor has some inherent capacitance in it due to the distance between the individual windings. I've heard somewhere that if you place a permanent magnet close to a coil that it will behave like a capacitor and I was wondering...
I have thought about these questions, and although they seem easy I have different answers to them:
1) Consider a parallel plate capacitor with some capacitance C. The plates of the capacitor are connected to a battery that maintains a constant potential. If the plates are moved farther...
Hi, I've attached a diagram of the question. The real question reads differently, but I've done my own interpretation. The interpretation might be wrong/ right, but its left me thinking anyway. So, I'd appreciate any advice/ hints on how I might go about finding the capacitance. I have tried it...
I know that Electrostatic Potential at a point due to a point charge is defined as the amount of work done in bringing a unit positive charge to that point (working against the electric force)
But, I am unable to reconcile this definition with the phrases like "Potential of a conductor"...