# What is Capaci tors: Definition and 24 Discussions

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1. ### Electrons enter charged capacitor

I cannot understand. I think that the constant electric fields and the direction the electrons ahead of cannot change the speed, but I can’t be sure about that. I really hope that someone can help me on that, thank you very mouch.
2. ### Force needed to hold together a capacitor

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 recently learned about Electric displacement field and capacitors, and I have a question that how was the formula derived shown below (blue circle part)? Thanks!
4. ### After how many time constants is capacitor energy 1/4?

Homework Statement [/B] After how many time constants is the stored energy of a discharged capacitor one-fourth its initial value? Homework Equations [/B] (1) U = Q2/2C (2) U = Qmaxε/2 (3) q(t) = Qie-t/RC The Attempt at a Solution The solution can be correctly attained using the first...
5. ### Capacitor Electric Field in a Dielectric?

Hi, I was reading the capacitor and its operation and it is written there that when the DC is applied to the capacitor it becomes open circuit. The main mechanism behind this phenomena is explained as below:- "When DC voltage is applied the charge started accumulating on the plates of the...
6. ### If the AC EMF is 0 at t=0, then how does current pass through a capacitor?

Hi, I have a problem understanding the ac capacitive circuit, where Vc = Vm * sin(ωt), and, current leads the voltage, so at t = 0, v = 0 which means no emf, no pushing energy for the electrons, I think, then how current is max? what is the energy source that supplied the electrons with the...
7. ### Electric field in a capacitor with multiple dielectrics

Hi, I am trying to understand capacitors and have come across the example in the attached image. What I would like to understand is how to calculate the electric field at some distance x within the capacitor. With x>>R , x<R and x=R . The image is of two circular disks as the...
8. ### Fully filled capacitors with parallel dielectrics problem

consider that we have two dielectrics inside a capacitor as shown in the picture, let0s consider also that Q is the charge of the capacitor and d the distance between the two plates , the first dielectric occupy a surface of S/3 with a dielectric constant of er1 and the second a surface of 2S/3...
9. T

### Why are these capacitor in parallel?

The question (and image) that are puzzling me are the same as in https://www.physicsforums.com/threads/two-opposite-polarity-charged-capacitors-in-series.723158/ It says that the capacitors are in parallel, but why? I can´t understand this point, and it certainly seems as if they are in series...
10. ### Capacitors charged in parallel

Homework Statement Capacitors C1 = 6.97 uF and C2 = 1.54 uF are charged as a parallel combination across a 281 V battery. The capacitors are disconnected from the battery and from each other. They are then connected positive plate to negative plate and negative plate to positive plate. A)...
11. S

### Electricity (charge on capacitor in circuit)

Homework Statement A capacitor of is connected as shown in the circuit. The internal resistance of the battery is Amount of charge on capacitor plates will be : Homework Equations no relevant euqations given. The Attempt at a Solution I don't even know how to begin with the question:(...
12. ### What Capacitor Size Is Needed for a Rapid Discharge Application?

This is a pretty simple question, one that there is likely a simple answer to. So, I need to use a capacitor as a rapid dump battery, not a filter or anything. The required current for this application is 1.7 Amps, and only 0.23 volts is necessary. I'm not too sure as to what amount of farads a...
13. ### Understanding Cylindrical Capacitors: Charged vs. Disconnected

Homework Statement Normally this style of question wouldn't be too bad, however the 2 different parts confused me. Surely once set to a potential V, it would stay at that potential - it doesn't need to stay connected How are the 2 parts any different from each other?
14. ### What is the advantage of CNT and graphine capacitors

i'm fairly new to the world of electricity an was just wondering why capacitors with graphine and carbon nanotubes are better than conventional. is it just due to increased surface area?
15. ### Discharging capasitors and it's general electrical propertie

It's just that I've never properly sorted this confusion of mind, so i would like to sort it out so it 2 different capacitors are in series with a resistor: (let's say 0.15F, 0.45F, 150M ohm) 1. both current and voltage drops exponentially 2. capacitance on capacitors remain same over time? 2...
16. ### How Does Introducing Different Dielectrics Affect Capacitance?

Homework Statement A parallel plate capacitor having plates of area S and plate separation d, has capacitance C1 in air. When two dielectrics of different relative permittivities ( ε1=2 and ε2=4) are introduced between the two plates as shown in the figure, the capacitance becomes C2. the ratio...
17. ### Find the interaction potential energy

Homework Statement 2 concentric shells are placed with inner shell having charge q and outer charge -q, with radii a and b respectively. Homework Equations don't know The Attempt at a Solution the question asked me to find self energy of the 2 shells and interaction potential energy,i found...
18. ### Kirchoff's Loop Rule Involving 2 Resistors and a Capacitor

A 5μF capacitor is connected in parallel with a 2MΩ resistor and the combination is then connected in series with a 1MΩ resistor through a switch to a 12V battery. Find the time taken for the voltage across the capacitor to rise from zero initial value to 2V after the switch is closed.From what...
19. ### Is Work Required to Move Capacitor Plates Apart?

If I have a capacitor and I maintain the potential difference between the two plates as I move them apart would I have to do any work (other than mechanical work) to move them apart? my logic tells be I shouldn't have to as I'm not doing any work again the potential field? Just wondered what you...
20. ### How I find value of U on R2 long time after switch is closed

https://qph.is.quoracdn.net/main-qimg-c22d8aa4be4fc2ed9b2f1c7060982e04?convert_to_webp=true How to find value of U on R2 long time after switch is being closed? Capacitors are charged so there is no current going through? Or? I used kirchof rule so i get Uo+Uc1-U=0 U=Uc1+Uo...
21. ### High voltage capacitor defibrillator

If defibrillation is not required is there an alternative method to save the enrgy for the next needed defibrillation rather than to discharge the capacitor using a resistor ?
22. ### Setting up differential equations for voltage

Let V1 be the voltage across C1 and V2 be the voltage across C2. I want to solve for V1 and V2 as a function of time. My idea was to use dV1/dt=I1/C1 and dV2/dt=I2/C2. Then using circuit rules i can express I1 and I2 as functions of V1 and V2 and substitute them into the previous diff eqs...
23. ### What is the final voltage that a capacitor charges towards?

The related question says:[PLAIN]http:// The capacitor 1 is initially charged by having the flying lead attached to point C. Then, the flying lead is moved to point D. Capacitor 1 discharges. C2 has no charge intially. When the flying lead is attached to D, which one of these statements is...
24. ### How Does Reconnecting Charged Capacitors Affect Their Charge Distribution?

Homework Statement Capacitors ## C_1 = 4 \mu F## and ##C_2 = 2 \mu F## are charged as a series combination across a ## 100V## battery. The two capacitors are disconnected from the battery and from each other. They are then connected positive plate to positive plate and negative plate to...