The figure is a cross section through three long wires with linear mass density
ID: 2098037 • Letter: T
Question
The figure is a cross section through three long wires with linear mass density 54 g/m . They each carry equal currents in the directions shown. The lower two wires are 4.0 cm apart and are attached to a table.
http://www.chegg.com/homework-help/questions-and-answers/figure-cross-section-long-wires-linear-mass-density-41-g-m-carry-equal-currents-directions-q1842587 (this link is only intended for the image. Please disregard the numbers in this link.)
What current I will allow the upper wire to "float" so as to form an equilateral triangle with the lower wires?
Explanation / Answer
mg=2FCos30
0.054*9.8=(2*B*I^2*Cos30)/r -------------eq 1
r=2tan60=3.46cm -------(2)
substituting (2) in eq 1
0.054*9.8=(2*2*10^-7* I^2 *1.732)/(2*0.0346)
solving for I we get, I=229.91 A -------- Ans
I understand that the solution would have been more clear if the diagram was visible, but I'm sorry I tried everything and don't understand why isn't it showing.