physics
posted by Jenny .
Two rigid rods are oriented parallel to each other and to the ground. The rods carry the same current in the same direction. The length of each rod is 0.85 m, and the mass of each is 0.077 kg. One rod is held in place above the ground, while the other floats beneath it at a distance of 8.2 103 m. Determine the current in the rods.

The force (per unit length) Fₒ of interaction between two currentcarrying rods is
Fₒ = μₒ•I1•I2/2•π•x,
μₒ =4• π•10^7 H/m, I1 =I2 = I, x = =8.2•10^3 m.
F = m•g/L,
Fₒ = F ,
μₒ•I²/2•π•x = m•g/L,
I = sqrt (m•g•2•π•x/ μₒ•L) =
= sqrt(0.077•9.8•2•π•8.2•10^3/4• π•10^7•0.85) =191 A