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anonymous 5 years ago can anyone explain the charging process of capacitor to me? :(

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1. anonymous

When u have a current source, the capacitor gets a constant amount of charge per time until - well, until its fully charged. When dealing with a voltage source (most of the time you are), you have to consider that the resistance of the capacitor is theoretically 0 in the beginnning and goes towards infinity with time. Thus - cause of ohm's law, the current (being charge per time) gets lesser and the charging kinda slows down. Theoretically, it takes an infinit amount of time till you're finished with the charging. You can calculate the voltage on the capacitor with: $V_c(t) = V(1-e^{-t \over RC})$ sry for my bad english...

2. anonymous

RC is often called tau - it's the so-called time constant of the system. A Capacitor is practically considered fully charged after 5 tau.

3. anonymous

ok so basically its just a capacitor connected to a power source supply, it charges up until the emf equals to the emf of the supply?

4. anonymous

Ahm - i don't know about the US, but I never heard of 'emf' before and had to look it up - not sure, but I think it's obsolete - why not just call it voltage? ( i think it's a bad name, cause you might be tempted to think it has something to do with force, when it absolutely has not). Anyhow - yeah, the Voltage at the capacitor is the same (negative sign of course) as the Voltage of the source at the end. Dont forget about the resistor when drawing it (no source is ideal). ;)

5. anonymous

ok, do u hav a summary of eqn's for capacitor charging and discharging? : )

6. anonymous

hmm - nope, sorry. Discharging is just the other way round: $V_c(t) = Ve^{-t \over RC}$ I guess, you could just look it up on wikipedia... haven't found a really good pdf or something online...

7. anonymous

charging action of a capacitor will be clear if u look at the basic level of the capacitor. there are two surfaces either plane or curved. these plates are charged by electrostatic induction. but we only give charge to one of these plates the other plate gets charged by induction. now to charge a capacitor we need to apply potential. after three steps of charging the capacitor is able to charge beyond the potential. and then we say that the capacitor is charged. it basically increases the potential by acquiring more charge. it is possible as where ever we have charge potential exists.

8. anonymous

I recommend you watch this video lecture by MIT's Prof. Walter Lewin, http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/lecture-7-capacitance-and-field-energy/ It will surely help you.

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