Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-L] Charge division on Spheres.



I reasoned in this way: for Q charge, C capacitance, V voltage, R radius

Isolated spheres have charge Q1 = C1 V1 Q2 = C2 V2
Connected spheres at equipotential have the same charge distributed onto connected spheres of combined capacitance C1 + C2

So Carl's first assertion is self-evident: it is the second sentence beginning "Hence..." that troubles me: that an equipotential should demand that
Q1/R1 = Q2/R2 rather than (my misunderstanding): Q1/C1 = Q2/C2

Is there some simple way to help me understand this result of equipotential on capacitors?
Is it the result of stored energy loss at the moment of connection?
Forgive my too strong grasp of this mistaken concept....


Brian W



On 5/2/2017 7:40 PM, Carl Mungan wrote:
Connecting with a wire makes the whole thing one conductor and thus an equipotential. Hence V/k = Q1/R1 = Q2/R2. -Carl

On May 2, 2017, at 8:29 PM, brian whatcott <betwys1@sbcglobal.net> wrote:

I lately took to writing responses on the Quora Q&A site for recreation. I rarely stray from electronics and one or two othersubject areas where I have some insight. But the other day, withinternal alarm bells ringing, I strayed into a basic physics question,where some high-schooler (?) transcribed a question directly from somequestion paper, as they sometimes do.

You will recognize it, I expect. Two spheres of 4 and 6 cm radius are charged to 80 and 60 uCoulomb respectively. How is the charge redistributed when the spheres are connected with a wire? I answered on general principle, in this way: the charge is redistributed in proportion to the spheres' surface area. 4^2 / (4^2 + 6^2) X (80 + 60) uC and 6^2 / (4^2 + 6^2 ) X (80 + 60) uC. about 43 : 97 uC I was surprised to find (when I finally checked) that the charge division (as given in online sources) is proportional to spheres' radii, not area. 56 : 84 uC How was I so easily falsified? Brian W

_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l

-----
Carl E. Mungan, Professor of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/

_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l

---
This email has been checked for viruses by AVG.
http://www.avg.com