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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Europan Ocean on 14/03/2015 11:58:28

Title: Capacitor calculation in micro farads?
Post by: Europan Ocean on 14/03/2015 11:58:28

Good day.
Capacitors in series gain distance between plates and lose capacitance and so is the calculation, C total= 1/C1+ 1/C2?
And in parallel increase plate area so, C total= C1 + C2?

In micro farads.

Title: Re: Capacitor calculation in micro farads?
Post by: Colin2B on 14/03/2015 12:37:37

Quote from: Europan Ocean on 14/03/2015 11:58:28

Good day.
Capacitors in series gain distance between plates and lose capacitance and so is the calculation, C total= 1/C1+ 1/C2?
And in parallel increase plate area so, C total= C1 + C2?

In micro farads.

Almost right.
For series 1/C_Total=1/C₁+1/C₂
Parallel is correct

This works for any units of Farads, milli, micro, pico, just keep them all the same.

Just a note, for series capacitors it is not really correct to say the plates gain distance and lose capacitance, it is the charge on the plates and the potential difference which are the significant factor.
I'll leave you to work that through.

Title: Re: Capacitor calculation in micro farads?
Post by: syhprum on 14/03/2015 19:40:35

Am I right in assuming that if I have a charged plate capacitor containing e=cv^2/2 and pull the plates apart v increases to reflect the energy used to pull the plates apart ?

Title: Re: Capacitor calculation in micro farads?
Post by: chiralSPO on 14/03/2015 19:56:49

Yes, as long as there is no circuit for the charge to go through (isolated capacitor)

I believe there are some railguns (or Gauss cannons) that make use of this effect by using an explosive charge to propel the charged plates apart at the right before the capacitor is discharged into the weapon...

Title: Re: Capacitor calculation in micro farads?
Post by: Bored chemist on 14/03/2015 21:53:19

That is how one of these works
http://en.wikipedia.org/wiki/Electrophorus

Title: Re: Capacitor calculation in micro farads?
Post by: Colin2B on 14/03/2015 22:30:30

Quote from: syhprum on 14/03/2015 19:40:35

Am I right in assuming that if I have a charged plate capacitor containing e=cv^2 and pull the plates apart v increases to reflect the energy used to pull the plates apart ?

I think this is what was confusing the OP, this is an effect seen in the charged plate experiment rather than an effect of connecting the capacitors in series. It might at first sight appear the plates have been separated by distance rather than by circuitry.

Title: Re: Capacitor calculation in micro farads?
Post by: Europan Ocean on 15/03/2015 03:36:04

Thanks for that.

Title: Re: Capacitor calculation in micro farads?
Post by: alancalverd on 15/03/2015 09:56:26

Quote from: syhprum on 14/03/2015 19:40:35

Am I right in assuming that if I have a charged plate capacitor containing e=cv^2 and pull the plates apart v increases to reflect the energy used to pull the plates apart ?

It's the principle behind the VandeGraaff generator, the Wimshurst machine, and (with a few complications) thunderstorms.