Capacitance Definition and 903 Threads

I keep reading the amusing lectures from Feynman on Electrodynamics. In particular in Lecture 5-8 figure 5-10, he argues that touching a charged hollow sphere externally with a litte metal ball will cause the ball to pick up charge from the charged sphere (contrary touching the hollow sphere...

Hello, I have some doubt on the representation of the physical model. I'm not sure about the number and value of the capacitance to be used. I solved the exercise using this model (see figure) and i would like to know if the solution is correct or if there is something to fix. Regarding the...

I did make the problem simpler by looking at the the part from d/2 down the upper plate here are my initial parameters I am making my size step be h since lowering it may make calculating harder I am especially getting weird results for the field and capacitance R = 0.1; % Radius of the...

Say I build a parallel capacitor from two 10cm x 10cm aluminum foil with one sheet of writing paper in between as dielectric. I press the foils together with a weight and a flat piece of plastic/glass. I can power on a 6VAC incandescent bulb with a 6VAC power supply. Now if I connect my...

I want to calculate the capacitance of this system between the points x&y. So suppose I give a charge Q to the outermost shell and -Q to the innermost shell. To find the capacitance C, I try to find the potential V between the outermost shell and innermost shell . To find V ,I integrate the...

A friend of mine sent me this problem about finding the capacitance. We have three concentric shells of radius a, b, c. And we've to find the capacitance between x and y. I need help. Thank you

When I write ##X_C=\frac ui=\frac{U_\mathrm m \sin \omega t}{I_\mathrm m \sin \left(\omega t+\frac{\pi}{2}\right)}##, it should be ##\frac{U_\mathrm m}{I_\mathrm m}##, but it isn't. Why?

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...

Why is it that, due to symmetry, ∆V2 = 0 and ∆V1 = ∆V4 = ∆V5 = ∆V3? I don't really understand the reasoning behind the simplification. Thank you.

I have attached my solution. Unfortunately, after plugging in the values, my answer is 4 times more than the expected one. What am I missing?

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

Because of the plate P, the capacitor becomes a piece of conductor. It contains zero net charge and has 0 potential difference. Hence, the capacitance is ## \frac 0 0 # # that is undefined. The capacitance of a capacitor is defined as its capacity to store charge when a potential difference is...

I don't understand how they got from the previous step to the next step of the derivation circled in red: Many thanks!

There are 3 parallel paths: one through 4.0 µF, one through 6.0 µF, and one through 5.0 µF and 7.0 µF. Why wouldn't there be another path through 4.0 µF, 7.0 µF, 5.0 µF, and 6.0 µF? Also, what determines the direction of current flow when there is a diagonal across parallel paths? Thank you.

I thought that if the slope of the T versus R graph is 4.00μF, then the capacitance would be 4.00μF but it says that's wrong. I know I'm doing something wrong but I'm not sure how to approach this problem. Can someone help?

You can find the impedance for each of the three positions with V/I. However I'm not sure how to find the inductive and capacitive reactance. Thanks for your help.

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

T=R/C So: 0.003s=R/100μC R=3*10^-7Ω I am really confused with the equations I have to use

[Mentor Note -- thread moved to the schoolwork forums] Hi. So I'm a Physics HL student in IB and I'm designing a circuit for my Physics IA. (think of it as a lab/project if you're not familiar with IB) I'm required to have an independent variable of 7 dif. values and a dependant variable. For...

The following is the question and the solution to the question. I understand the solution to the part where you find the Ceq and derive Qeq from the equation Q = Ceq*V. However, I do not understand where V1 = V0-V2 come from. When calculating the minimum voltage, how do you come up with the...

Into a project I am working is use 12Vdc SMPS to power an audio amplifier and some more components. We have no “noise” on that stage. Then I use a step down converter to convert the 12V to 5V and power a mic preamplifier (Respeaker – usb Mic array) and a development board. There is a lot of...

Hello, all. First, I want to apologize if this is not the correct forum or area of the forum for this question. Please direct me if I should be posting this somewhere else. I have some questions regarding what I believe is best described as the "theory" of electrical capacitance. As my...

I've been able to prove the following inequality $$\frac{2\pi\epsilon_0}{\log\left(\frac{b_1b_2}{a_1^2}\right)}\leq C \leq \frac{2\pi\epsilon_0}{\log\left(\frac{a_1a_2}{b_1^2}\right)}$$ but have no clue how to obtain exact value. Can someone check whether this inequality is correct and show how...

Is there any way to measure the capacitance of a capacitor indirectly using a multimeter that does not have the option to measure capacitance directly?

NOTE: THE C1 that is 120 microfarads is meant to be C3. What I did first was find equivalent capacitance of C2 and C3 by doing (40)*(120)/(40+120)=30. Then I found Ceq by doing (20)*(30)/(20+30)=12. For the resistance I did 6*3/(6+3)=2, for R2 and R1. Then to find Req I did (5)*(2)/5+2= 10/7 Am...

Hello there, I believe here I need to find the capacitance of the junction between the P-doped gate and N-channel. Then I could find the RC time constant although I am not sure if there's something more I need to find the speed of the JFET? What I'm unsure of is the depletion width h to use...

How could we prove mathematically that the capacitance does not depend on charge? I tried to find this proof in the internet but I was not able. Can you guys help me?

Imagine the two terminal of a *parallel-plate capacitor* are connected to the two terminal of a battery with electric potential difference #V#. If the capacitance of the capacitor is #C#, and the area of each plate is $A$. In this process would the energy lost by the battery and the stored...

The geometry of the capacitor can be either cylindrical or spherical.

Hey guys! I'm having trouble with the solution that I arrived at. Through boundary conditions I'm able to determine ##\vec{D}## as $$\vec{D}=-\frac{4Q}{R_0^2}\hat{e_z}$$ (In CGS units) Trough that I'm able to get the electric field as $$\vec{E}=-\frac{1}{\epsilon(r)}\frac{4Q}{R_0^2}\hat{e_z}$$...

like the picture, two adjacent hemispheres（radius R, distance d, assume the charge is ±Q of each side（assume evenly distributed）, can we calculate its capacitance?

Hi friends, I have simulated two circuits, one is an RC filter and other is a Capacitance multiplier. My aim of experiment is to validate a decrease in Iout (load current) of CM circuit as compared to load current in RC filter circuit. Theoretically, Iout (CM circuit) < Iout (RC filter) Vp-p...

Hello. I have a question related to capacitance. here is another mechanical solution to harness wave energy. Can changing capacity of the capacitor be used to harness wave energy? Let's say we envelope conductive plates in plastic and submerge them in the ocean and the water in between them...

This is not my homework. I took it upon myself to answer a textbook question for mental stimulation. I wanted to know if someone can verify if these were the correct values that needed to be solved for, process, and final answer, and if not, what needed to be considered. For the initial...

A solution I found online claims that the effective capacitance between the middle and inner shell can be seen as: C (effective) = C1 + C2, where C1 is the capacitance between the inner and outermost shell, and C2 is the capacitance between the middle and outermost shell. Apparently C1 and C2...

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...

I would like to ask about the behavior of a MOSFET as a capacitor, particularly at the onset of inversion/weak inversion - see Fig 2.6(c) At this stage in Fig 2.6(c), there is positive charge at the gate metal/poly contact, then an insulator oxide and then negative ions (positive holes have...

Could anyone tell me the capacitance of a one food diameter metal sphere. I know that this is a one terminal component but it still should have a capacitance. If a charge of Q is small and a 6 inch radius is drawn about the point then that 6 inch radius ( 12 in diameter ) should have a...

I am given the answer is 2J and I know how to get there with U = q^2/2C. But what I don't understand is that why is the energy not conserved here? How can energy loses just because the capacitance is doubled?

Initially, I thought to apply the image charge theorem, but I don't know how to continue. Someone could give me some indication on how to solve the problem? Thank you.

Could somebody check my solution?

When we have electrical resistance it is based on dissipation of energy, when we have reactance it is a consequence of charge accumulation in capacitance. Together they form impedance. But let's consider what exactly is responsible for dissipation in case of resistance? Is not it because of...

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...

The capacitance must be found, that is: ##C=\frac {Q}{V_a-V_b}##. Let ##\vec{E_d}## and ##\vec{E_v}## be the electric fields due to the zone with dielectric and the zone without dielectric respectively. In the case of a spherical capacitor with a vacuum between its plates, it is easy to...

Using: $$i(t)=\frac{U}{R}.e^{-\frac{t}{RC}} As the power is constant, then the current will be constant, so: t/RC is constant I don't know how to proceed anymore. I think you should use some derivative, but I'm still very new to that part, so how can I proceed?

Consider a circuit with a witch, capacitor and an AC voltage source. The sinusoidal AC voltage source is depicted in the following graph: We know that, ##Q = CV## ##\frac{dQ}{dt} = C \frac{dV}{dt}## ##i = C\frac{dV}{dt} \tag{1}## So from the graph, the voltage increases rapidly around ## t =...

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...

I asserted C3, C4, and C5 to be in series. **I found the capacitance of "C3-4-5" to be 1.67x10-6 F. This I did by using 1/C = 1/C3 + 1/C4 + 1/C5 Then I noticed that I had another series circuit of "C3-4-5" and C1, and C2. Again, I used a similar formula. I obtained an equivalent capacitance of...

Assuming we have an infinite plane capacitor,where the upper plate is charged positively and the bottom layer is charged negatively. Now we know the field outside the capacitor is zero so we can't tell if the positive charge is on the upper plate or the lower plate. But, if we place it inside...

Please can you have a look at the file at point me in the right direction if I'm wrong. Thank you