# capacitor

1. ### A circuit with switches, capacitators and resistors

To solve this question first I calculated the potential energy the capacitor A stored. It's equal a: Ca.V²/2. Ok, so when switch S1 is open and S2 is closed I calculated the equivalent capacitance as if they were in series --> 1/Ceq = 1/Ca + 1/Cb --> Ceq = (Ca.Cb)/(Ca+Cb). So I used the formula...
2. ### Determine the effective current value in the circuit with C and R

Given: U = 220 V f = 50 Hz r = 20 Ohm C = 100 μF Find: I Solution: 1) Xc = 1/(ω*C) = 1/(2*π*f*C) = 1/(2*π*50*10^-4) = 31.83 Ohm 2) R_eq - equivalent resistance R_eq = (r*Xc)/(r+Xc) = (20*31.83)/(20+31.83) = 12.28 Ohm 3) I = U/R_eq = 220/12.28 = 17.9 A True answer given in the textbook is 13 A...
3. ### Dielectric interface plate capacitor at angle alpha

Consider a plate capacitor with a dielectric interface (\epsilon = \epsilon_0*\epsilon_r, thickness=d) tilted at the angle \alpha . Outside the interface \epsilon = \epsilon_0. Without dielectric interface is the field \vec{E}=E_0*\vec{e_z}. Determine the E-field inside and outside the...
4. ### Calculating the capacitance of a capacitor

Summary: Two plates side by side, not parallel to each other. Hello everyone, Purpose of this capacitor is to detect changes in water level. It is constructed of a single copper plated pcb on which middle I have made a 1 mm of space separating now two copper plates on a single pcb. So, plates...
5. ### I Gauss' law in Dielectrics

[PAGE 1] [PAGE 2] [PAGE 3] so in the 2nd page,when the dielectric material is introduced the gauss's law becomes $$\oint _ { S } \vec { E } \cdot \vec { d S } = \frac { ( q - q _ { i } ) } { \epsilon _ { 0 } }$$.But my question is why the ${ \epsilon _ { 0 } }$ is in the equation.Shouldn't...
6. ### Novice question about Relays, Capacitors, and Diodes

Hello, In regards to this relay, TQ2SA-1.5V Panasonic 2 Form C AS Single side stable, 1.5VDC 2A DPDT NON-LATCHING SMD Relay Link to Relay PDF 1 of Relay PDF 2 of Relay (specifically pages 5-6) is attached at the bottom as a pdf file. I was previously told that I would need to wire a IN4001...
7. ### Determine the capacitor value so that this circuit is in resonance

L=100mh=0.1H ω=10^3 rad/s -> f = 159Hz XL= ωL= 2πfL= 2π*159*0.1= 99.90 Ω Z parallel = [(XL∠90º)*R2] / [(XL∠90º)-R2]= 37.13∠-21.8º XC= 1/ωC= 1/(2 π f C) I dont see how I am supposed to get to C
8. ### Capacitance of a circular capacitor with two parallel dielectrics

Hello, the problem is better illustrated at the picture below. The capacitor is isolated, with an initial charge Q0. I understand that Q0 does not distribute along the plates homogeneously. How could it be solved with the equivalent parallel circuit?
9. ### I RC charging - intuition behind equal dissipated energies?

Assume that a resistor R charges a capacitor C, whose other terminal is connected to the ground. The charge at time t = 0 is assumed to be null and the supply voltage is equal to V. We have, as is well known, $i = \frac{V}{R} e^{-\frac{t}{RC}}$. Integrating $\frac{i^2}{R}$ between t = 0 and...
10. ### What is the voltage across this capacitor, inductor and resistor?

I can solve for the questions in completely series or parallel circuits however having the capacitor and inductor in parallel while the resistor stays in series is stumping me completely.
11. ### B Capacitor and electrostatic field

Is there any electrostatic field around the leads of a charged capacitor? Let's take just the negative one. If I take a piece of tissue and put close to that terminal it will attract or repel the paper? And if not, why?
12. ### How does a Capacitor protect against voltage spikes?

Hi Everyone ! I have one confusion regarding the role of the capacitor in the circuit. How does the capacitor protects the circuit from the high voltage spikes. If the capacitor is connected from the circuit with battery. And sudden high spikes come then the capacitor is charged and the energy...
13. ### I How to treat the "ideal" plate capacitor more rigorously?

Hi. The derivation of the capacity of an ideal parallel-plate capacitor is inconsistent: On the one hand, the plates are assumed to be infinitely large to exploit symmetries to compute an expression for the electric field, on the other the area is finite to get a finite expression for the...
14. ### Final potential difference of a 2 capacitor system

Homework Statement An isolated parallel-plate capacitor of area $A_1$ with an air gap of length $s_1$ is charged up to a potential difference $\Delta V_1$ A second parallel-plate capacitor, initially uncharged, has an area $A_2$ and a gap of length $s_2$ filled with plastic whose...
15. ### I A change in the dielectric constant changes the current or voltage?

hi everyone! i am not into physics, but need it now,i am a programmer workin on an IOT project...so kinda need help. i want to use a capacitor to see what passed between two plates...knowing, it is the change in dielectric after certain intervals......how do i measure the change at the other...
16. ### Shell in a cylindrical capacitor

Homework Statement There is a capacitor (llenght $L$) made of a conductor (cylinder of radius $R_1$) and a cylindrical surface (radius $R_2$). It is charged with a potential $V_0$, then it is isolated. (There is vacuum between $R_1$ and $R_2$) Now we insert a cylindrical...
17. ### Energy dissipated in the resistors in a 2 mesh RC circuit

Homework Statement Hi mates, I have problems solving the third part of this exercise, I've already done all the previous calculations. Given the following circuit, where the switch S is open, the power supply = 50 volts and: The initial charge in the C capacitor: QC = 0 coulombs The initial...
18. ### B Confused by capacitors and potential energy

Hi I was reading about capacitors and potential energy. But the equation seems counter to how i thought. For potential energy you have: U = Q^2 / 2C or U = CV^2 / 2 But doesn't this suggest you lose potential energy the more capacitance you have? Since in the first equation as C increases U...
19. ### Engineering Finals Study Time! A Two Source Circuit w/Inductor, Cap, and Resistor

Homework Statement Homework Equations Z = √(XC2 + XL2) XL = 2πƒL XC = 1 / 2πƒC I = V/Z The Attempt at a Solution First off, thank you for all of the help this semester. I'm sure you'll be seeing questions from me in the spring also. Here is how I'm thinking about this problem: 1. Using the...
20. ### Can we extract energy out of a capacitor in the ocean?

Hello, sorry about my english it's not my mother tongue. I hope this is the right section to place this. 1. Homework Statement A cylindrical capacitor is placed in the sea so that when a wave comes (the water goes up), the water becomes the capacitors dielectric, when the wave has passed (the...
21. ### I Question on the work done while charging up a capacitor.

So the work done when charging up a capacitor is $dW=VdQ$ However, when we add a charge $dQ$ to the capacitor, $V$ also changes accordingly, so I was wondering why the work done wasn't written as $dW=VdQ+QdV$ (one that also takes into account t he change in $V$). Thanks in advance.
22. ### Combination of capacitors

Homework Statement Between the plates of parallel plate condenser having charge Q,a plate of thickness t1 and dielectric constant k1 is placed.In the rest of the space,there is another plate of thickness t2 and dielectric constant K2.The potential difference across the condenser will be...
23. ### I Capacitor with Irregular size dielectric

Is it possible to make a capacitor with a dielectric not of the same size with its conducting plates?
24. ### Calculations for a capacitor charging from another capacitor

Hi all, I'd appreciate help in calculating the voltages in the circuit shown. I thought it should be fairly straight forward, but it has me stumped. This is a sample-and-hold circuit for an ADC -- the switch is closed to charge the hold capacitor with the sample voltage and then opened to...
25. ### B Voltage vs charge?

If voltage is the difference in charge between 2 points, then why for a capacitor of a larger area or thinner dielectric cross section, do they say that it can store more charge given the same apppied voltage? Isnt voltage the difference in charge between 2 points? So if you can store more...
26. ### B Electromagnetic coil and capacitors vs resistance

I'm not really sure if this is even scientific but while calculating how much energy is stored in electromagnetic coils and capacitors, pretty much the same formula is used: For electromagnetic coils it's U=0.5LI2 For capacitors it's U=0.5CV2 Why I think they're the same is that in a sense L to...
27. ### Find the transient current in this circuit

Homework Statement Homework Equations The Attempt at a Solution I often do circuit. But still there is always stuff i dont get.. I was asked to find 1) I1 I2 I3 immidiately after S closed 2) I1 I2 I3 after sufficient of time 3) I1 I2 I3 immidiately after S opened Just give me clue please...
28. ### Why is a capacitor a generator of lagging reactive power?

An ideal capacitor has power factor of zero degree leading as current leads the voltage in capacitor.But it also means that capacitor is generator of lagging reactive power.What does that mean.How does it do so.Capacitor is used for reactive power generation at inductive load sites.
29. ### Making Capacitance the subject of discharge equation

Homework Statement I have to rearrange the equation V=lnVo -t/RC to calculate C. The gradient from graph = -1/RC Homework Equations The Attempt at a Solution I got R/C=ln(Vo-V)/t but the answer I get is wrong
30. ### Find the Voltage in the parallel resistor-capacitor circuit

Homework Statement C1 = 4 micro F C2 = 8 mF R1 = 4 ohm R2 = 8 ohm V = 12 Questions : 1) Find current I when S not closed 2) find Vb, when Vc is 0 3) find Vd, when Vc is 0 4) total charge move from B to D Homework Equations Vf - Vi = F.d/q (not sure this below is useful equations) I = E/Z E...