Charged balls suspended by strings in electric field

[Kadaj]

Hi,
I have a problem here that I'm having trouble with, I attempted to do it by using equations dealing with magnetic fields and electric fields, but then i had to consider the tensions of the strings and the components and became lost. Can anyone help me?

Thanks in advance,

Here is the problem:
http://img.villagephotos.com/p/2004-9/824584/stupid5.jpg

Thanks again

 

[OlderDan]

Consider the weight of some length of the wires. The tension in the string has to support the weight and pull the wires together. If T is the tension, the weight is T cos (7.5) and the horizontal force is T sin (7.5) The horizontal force from the tension is equal to the force of repulsion due to the currents.

 

[Kadaj]

ok, I did what you said and got the current as 91.8A, but is this right? I found the horizontal force to be 1.29 and the length between the wires to be .0259 meters, then i used the equation, F/L= (permeability of freespace)(I^2)/ 2(pi)r, and I took the force and multipled it by the .050 kg/m then solved for the I in the equation. Is this right? or is there something I;m doing wrong.

Thanks for the help

 

[OlderDan]

Chances are pretty good when you do a multiple choice question and get exactly one of the answers, you have done it right. You have the right equation for F/L. I don't know what your units are for a horizontal force of 1.29. Do you mean force per unit length in N/m? Something else? I don't see 1.29 coming out of the numbers. The horizontal force on each wire is about .132 times the weight, with the tension in the string being about 1.00863 times the weight. Check your calculations, and then believe them.