Read about capacitor | 185 Discussions | Page 1

  1. M

    I Some questions about capacitor discharging

    why does the voltage of the capacitor eventually go to 0 when discharging the capacitor? I heard that's because "current starts flowing when discharging", but how exactly does that lead to V going down? I know that I = C * dV/dt, but that doesn't seem to help me understand why V goes down (which...
  2. P

    Olympiad AC Circuits Problem

    The problem is shown below: (I am only asking about part b) ^Above is the problem. Below is the solution to part b. They have claimed that we can set potential at C = D = u(t), and A=B=0. Why is this claim true? What I realise: By applying Kirchoff's across ACDB, Voltage across C1 = Voltage...
  3. J

    B Question on capacitors -- Can two charged conductors have a potential difference between them if they have equal charge?

    Hi, I found the following question in a physics book, and so dusted off my 30yr old knowledge on capacitors and tried to answer it. The question is as follows :- "Suppose two nearby conductors carry the same negative charge. Can there be a potential difference between them? If so, can the...
  4. lekh2003

    Electrical How to use capacitors in a Solenoid circuit

    I've been working on designing an experiment over the past few weeks as part of a school project, under the supervision of a teacher. I have designed a small low-power coil-gun. I have a coil of roughly 60m 24 AWG copper wire wrapped around a length of 2.5cm of clear PVC pipe. I tested the...
  5. G

    Capacitance of a spherical capacitor

    When I try to do Gauss, the permeability is not always that of the free space, but it varies: up to a certain radius it is that of the void and then it is the relative one. How can I relate them? I'm trying to calculate the capacity of a spherical capacitor. The scheme looks like this: inside I...
  6. Praveen1901

    Kirchoff's laws and capacitance

    Equivalent capacitance before and after remains the same. Now the 10F capacitor (which was initially connected in parallel with 20F) would have 30 C charge. Hence an additional 20C must have been supplied to it. The only path which may supply the charge is through battery. However this leads...
  7. Prabs3257

    Heat dissipated in a Resistor-Capacitor circuit

    I tried to conserve the charge on the left plates of both the capacitors as intially the total charge on both is 48 and at t=t0 the total charge is 36(on c1) +4V(V is the potential across c2) so i got V=3 and then i conserved the energy Initial energy on both capacitor = final energy on both +...
  8. K

    Discharging this capacitor in an RC bridge circuit

    The voltage source in the circuit below has been switched on for a long time when the switch S switches off. How long will it take before the current coming out of the capacitor has become less than 1 mA? My attempt: I am far from sure that my solution is correct. This is because i...
  9. eyespy

    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...
  10. L

    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...
  11. L

    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...
  12. akaliuseheal

    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...
  13. Hawkingo

    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...
  14. shushi

    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...
  15. baywa2

    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
  16. maxipoblete

    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?
  17. C

    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...
  18. Tesladude

    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.
  19. T

    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?
  20. Muhammad Usman

    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...
  21. G

    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...
  22. Zack K

    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...
  23. S

    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 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 do i measure the change at the other...
  24. F

    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...
  25. Eduardo Leon

    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...
  26. T

    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...
  27. Lapse

    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...
  28. M

    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...
  29. B

    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.
  30. Abhimessi10

    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...