A current balance is set up so that a mass of 20.0 mg on the upper wire restores balance?

Question

to the system when a current of unknown magnitude is sent through both wires. The wires are 26.5 cm long and have a center-to-center seperation of 0.0525 cm. Find the current.

Answer 1

use Ampere's law. The first wire sets up a B-field equal to

B=ui/(2πd) The force is Bil=ui^2l/(2πd)=
4πE-7*i^2*0.265/(2π*5.25E-4)=20E-3 ==>i=14.1A