Capacitance Definition and 903 Threads

Hi, In Spice, the capacitance between two points x, y is defined as follows: Cxy = - dQx / dVy for x != y Cxx = dQx/dVx Could anyone help me explain why it is defined like that? I know that C = dQ/dV but the formula above seems strange to me. Is my understanding below correct? Cxy =...

I have done no. 1, but I don't how to do no. 2. Someone, please help. Power source voltage e(t) = sqrt(2)*20sin2t [V], current i(t) = 5sin(2t - pi/4) [A]. 1. Find the values of resistance R, and inductance L. 2. Let V be the phasor of voltage v(t). Find the capacitance value of the...

Hello all! My friend and I are having a bit of a discussion. We did an experiment on liquid crystals as dielectrics with changing voltage, and we came across some weird conclusions (capacitance decreased with increasing voltage? odd. Our theory is that liquid crystals don't act as normal...

Hello! How do I calculate the capacitance of a twisted wire pair in 3D? The pair of wire would have two different dielectric(air and insulation) mediums and hence I am not able to figure out how to calculate it by hand. My plan was to create a 3D Model, mesh it and put it up in...

I have been given the exercise above which relates to an article we are reading. I can calculate all the results but I can't interpret them physically. I think my major problem is that I don't see how self capacitance is a physically measureable quantity. For a recap the self capacitance is...

I'm having a time figuring out how to solve this one, hope someone can help me out Homework Statement "Calculate the equivalent capacitance between X and Y on the circuit in the figure. C1=C3=C4=C5=8uF, C2=20uF" Homework Equations The Attempt at a Solution I can't figure out a...

Homework Statement Consider the circuit shown in the attachment. Capacitor C1 is first charged by closing switch S1. Switch S1 is then opened, and the charged capacitor is connected to the uncharged capacitor by closing S2. Calculate the initial charge acquired by C1 and the final charge on...

Find that capacitance of the system consisting of 3 dielectrics w/ length, l=1.0m, width, w= 1.0m and depth, d= 1.0 CM. ##k_1=1.5, k_2=2, k_3=2.5## *dimensions of conducting plates not given* Equations: Capacitance, ##C= Q/{\delta}V## Field in the dielectrics...

Homework Statement A cylindrical capacitor of length L consists of a solid conducting core with a radius R and an outer outer hollow conducting tube with an inner radius 3R. A voltage V_{ab} is applied between the two cylinders. Assume L >> R which means we can neglect edge effects. Given [L...

Homework Statement Two square metal plates with sides of length 0.1 m are separated in vacuum by 10-3 m. Find their capacitance. Homework Equations C = Q/V For a parallel plate capacitor: C = E0A/L The Attempt at a Solution If A is supposed to be the length of the metal...

Homework Statement The voltage across a capacitor with a value of 0.01 Farads is v(t) 100*cos(2pi60t). Find i(t),p(t),and w(t). Homework Equations i(t)=Cv'(t) [current] p(t)=i(t)v(t) [power] w= integral of p(t) [Energy stored over time] The Attempt at a Solution I was able...

1. One question I'm having a lot of trouble solving is this: The plates of a parallel plate air capacitor have an area of 100cm2. The capacitor has a capacitance of 3.5nF and is connected to a 12V battery. It is fully charged. Calculate the: a) separation of the plates b) magnitude of...

Homework Statement Metal sphere of radius R1 is surrounded by a concentric metal shell of inner radius R2 and outer radius R3. The dielectric is air. Calculate coefficients of capacitance for the given setup. Homework Equations Picture of the problem: The Attempt at a Solution...

Hi PF! I'm working on a portable heating circuit. I'd like to use an ultracapacitor charged by 2 AA batteries to increase the temperature of 2.25m of 1mm Nichrome wire by 34° in 6 seconds. The question is, what capacitance does the ultracapacitor have to have? Initial values: •...

Hi all, I have a simple circuit with a battery, resistor, and finally, the capacitor. Am I correct in saying that adding additional resistors will increase the charging time, because adding resistors will decrease the overall current? Thanks--

Hi everybody, i was working on a layout of a boost converter control i finished it but now i am trying to calculate the parasitic capacitance of interconnects of power switches after searching i found that i can do that with software like "Maxwell" or "fastcap" but i don't now if it...

I am doing a lab experiment in which I need to find the capacitance of an electrolytic cell containing water and of course hydrogen and oxygen ions. The cell has both a double layer capacitance as well as a pseudicapacitance. My initial studies show that I would use cyclic voltammetry...

is there a instrument used to detect under ground water using capacitance principle

I am stuck, can someone help me, please? I am not sure if I started the right way, it seems tedious :( The magnitude of V1 is 2 times greater than V2, and its phase leads π/2 ahead. The angular frequency ω of the power supply voltage is 5rad/s. Find the values of the resistance R and Capacitance C.

Homework Statement Consider two concentric spherical metal shells of radii 2m and 4m, situated in free space and carrying uniform surface charge densities of 20nC/m2 and 5nC/m2 respectively. Find the capacitance C=Q/ΔV of the spherical capacitor formed by the shells. Here Q is the total...

Homework Statement A 9.0 uF and 4.0 uF capacitors are connected in parallel, and this combination is connected in series with a 12.0 uF capacitor. a) what is the net capacitance? b) if 32 V is applied across the whole network, calculate the voltage across each capacitor. Homework...

Homework Statement Airbag Sensor To trigger the airbag, accelerometers are used. A simple sensor is composed of three parallel plates of the surface A, which are connected to a condenser system. The mass m of the middle plate can move between the two fixed outer Moving plates. She is...

I am in process of designing a homemade capacitance sensor and I'd like to have an approximation of the resulting capacitance of the following geometry. The plates are placed on the outer surface of a food grade plastic cylinder. The distance z between their edges is many times smaller than the...

A parallel plate condenser is connected with the terminals of a battery. The distance between the plates is 6 mm. If a glass plate (dielectric constant K=9) of 4.5 mm is introduced between them, then the capacity will become Ans 3 times how?

I understand that the dielectric constant of a perfect isolated charged conductor is infinite when its placed in an electric field (generally uniform)... Now I also know that when a conductor is placed between a parallel plate capacitor such that the distance between two plates in those...

Homework Statement Find the electric field in a capacitor with dielectric constant ε, then calculate the capacitance. For a parallel plate capacitor, two methods are usually offered. (M1) Add the electric fields from two infinite charge sheets, one with surface charge density σ, the other...

Homework Statement I'm almost embarrassed to post this, but insofar none of my searches online have yielded any results. My question is simply, given a parallel plate capacitor (for the purpose of simplicity let's assume that there are no edge effects) whose constituent plates have charge +aQ...

Homework Statement Calculate capacitance of a parallel plate but of made up o two media!? The parallel plate capacitor in the figure below is quarter-filled with mica (εr=6). Its remaining ¾ part is filled with air. The total area of the capacitor is 10 cm2 and the distance separating the...

Calculate capacitance of a parallel plate but of made up o two media!? The parallel plate capacitor in the figure below is quarter-filled with mica (εr=6). Its remaining ¾ part is filled with air. The total area of the capacitor is 10 cm2 and the distance separating the plates is 2mm. Find the...

I was reading the following thread at stackexachange. http://physics.stackexchange.com/questions/9830/tension-in-a-curved-charged-wire-electrostatic-force-does-wire-thickness-mat The first answer calculates the radial force using the capacitance of ring. Any ideas how the poster derived the...

I have read that if we have an isolated positively charged conductor, we can increase itself capacitance by bringing an identical conductor close to it and then earthing it, so, that the second conductor develops a negative charge and thereby helps in reducing the net electric potential on the...

Homework Statement This is my data of Irms and angular frequency, and I have to plot the graph and teacher told me that the gradient will be capacitor's capacitance? Homework Equations The Attempt at a Solution Did do anything wrong?

Homework Statement The electrical model of an operating AC induction motor yields an impedance, Z, of 18.65+j15.106Ω . What value of parallel capacitance is necessary to achieve a power factor of unity if the operating frequency is 60Hz? Homework Equations V=IR w=2pif P=VI The...

HI, please do not get me wrong, I am trying to grasp and learn when HV capacitors get dangerous and I am confused right now. Your help is extremely appreciated. Caps discharge their energy very very quickly and said THERFORE to be dangerous, but a Van de graaf also discharge its energy...

Hi, I need help with this. A non-conducting slab of thickness t, area A and dielectric constant κe is inserted into the space between the plates of a parallel-plate capacitor with spacing d, charge Q and area A, as shown in Figure 7.7.5(a). The slab is not necessarily halfway between the...

Homework Statement Draw the equivalent circuit for a lumped capacitance with dielectric losses that would be appropriate at RF frequencies. Homework Equations Possibly Xc=-j/ωC The Attempt at a Solution I do not really know what the question is asking. I know that a lumped capacitance...

Homework Statement "A capacitor is being charged from a battery and through a resistor of 20kΩ. It is observed that the voltage on the capacitor rises from 10% of its final value to 90%, in 15 seconds. Calculate the capacitor's capacitance. t = 15s R = 20kΩ Vi = 10% of max Vf = 90% of max...

Homework Statement Trying to calculate capacitance on an LC circuit Homework Equations L = 1.0H (solenoid inductance) i = 3.0 Ma (current in circuit) Q = 30μC (charge on capacitor) E = 4.5μJ (energy in oscillations) The Attempt at a Solution All I'm after is an equation for...

Homework Statement Part A Given 4 capacitors of the same capacitance C, (a) list all values of capacitance you could obtain by connecting up to 4 capacitors. (b) Construct a table with two columns: the first column contains all possible values of capacitance in increasing order, and the...

Homework Statement The charge center of a thundercloud, drifting 3.0km above the Earth's surface, contains 20 C of negative charge. Assuming the charge center has a radius of 1.0km Calculate the Capacitance of the system. Homework Equations C=8.85*(10^(-12))*A/d Where A is the area, D...

Homework Statement In the figure, C1 = C5 = 8.0 microF and C2 = C3 = C4 = 4.2 microF . The applied potential is Vab = 230V Homework Equations 1/Ceq=1/C1+1/C2+...+1/Cn(for series connections) Ceq=C1+C2+...+Cn The Attempt at a Solution The answer is 2.4x10^-6 So far I have...

Homework Statement A capacitor is to be designed to operate, with constant capacitance, in an environment of fluctuating temperature. As shown in Fig. 23, the capacitor is a parallel-plate type with plastic "spacers" to keep the plates aligned. (a) Show that the rate of change of capacitance C...

Homework Statement When the switch is closed, Potential drops to 40v across C1 & C2(Parallel series). Find the Capacitance of C2 Homework Equations Before switch is closed C1=300uF and holds a charge of Q1=3e4 uC V=100vAfter switch is closed V'=40vThe Attempt at a Solution V1=V2 So...

Homework Statement We have two conducting plates. One is moveable, the other is not moveable. The moveable has the charge of +1V. While the other plate has the charge 0V and is part of a enclosing envelopment. See fig: http://tinypic.com/view.php?pic=wb2onm&s=6 But when we move the...

So I'm trying to solve this kind of problem And I got stuck. Capacitor with power 2000*e^(-jPi/2) and connected to voltage u(t)=282,84sin(314*t+Pi/4). Determine the capacity. I know power is P=U*I, capacitance is C = 1 / Xc*w, from that u(t) we have that w is 314, so rearraning equation P =...

Homework Statement (see attachment) Homework Equations The Attempt at a Solution The self capacitance of an isolated sphere is ##4\pi \epsilon_o R## where R is the radius of sphere but I am not sure how to begin on this one. Any help is appreciated. Thanks!

Hello, So I am told that capacitance is a measure of how much charge can be stored in a capacitor. However, I don't have an intuitive understanding for why it is a relationship between charge and voltage. Can anyone help me in understanding it? I'm imagining one capacitor attached to a...

Hello, I am looking for some strategies for figuring out the best way to approach problems asking me to find the equivalent capacitance when given a daunting looking circuit with capacitors arranged in all sorts of funny ways, especially when issues come up of capacitors not contributing to...

Homework Statement I do not have a specific question, I am just wondering how one would go about finding the capacitance of three concentric spherical shells. Suppose the outer radius of the each shell is a, b, and c from the center outwards. Homework Equations E= -gradV C = Q/ V...

Homework Statement I'm asked to find 1)The capacitance 2)The electric field 3)The surface charge density 4)The polarization charge at the interface between the dielectrics. Of 2 set ups. The first one is a parallel plate capacitor which is half filled with a dielectric ##\varepsilon _1## and...