A quick question on a Phy2 E&M problem...

[duragezic]

I got a simple problem where I use Coulomb's law to find the electric force exerted between spheres. I got that fine, but how would having the spheres connected by a conducting wire affect the force between the two then? I searched the chapter many times and it made no mention of how that would change calculations. I'm assuming maybe it would knock out the 1/r2 part since they are essential right next to each other but that didn't appear to work. Any ideas?

 

[esun]

Well the wire would give them the same charge (so if you had a +1Q and a +3Q charge, then after connecting them it would be two +2Q charges). So then you have to just do the calculation with the new numbers.

 

[duragezic]

Hmm yeah sounds like that should be it cept that I'm not even coming close to the answer. The charges are 1.2E-8 and 1.8E-8 by a distance of .3. So I'm doing k(1.5E-8)(1.5E-8)/.09. The thing I noticed is that the answer is 1E-16 times the k constant, so I can kind of see the two E-8 charges being multiplied so the power is right but the numbers aren.t

It also adds that this is the force after coming to equilibrium.

 

[duragezic]

bump

 

[DrPizza]

duragezic..... are they both positive charges? (or both negative charges)? If so, then I agree with your post 2 above this....
But, if one is positive and the other is negative (attractive force), at equilibrium, I believe both would have a charge of .3E-8.

Hmmm.... all the .3's cancel out and you're left with E-16 times k....
I guess I solved your problem

 

[DrPizza]

oh, btw... Jellybeans?!!

I'd scream that in my class if you left out the units.