question.rb1 question :two_parallel_wires do2   kind :numerical3   describes "Two long and parallel straight wires A and B carrying currents of %{current_a} and %{current_b} in the same direction are separated by a distance of %{separation}. %{force}, in newtons?"4   given current_a: "8.0 A"5   given current_b: "5.0 A"6   given separation: "4.0 cm"7   asks force: "What is the force on a 10 cm section of wire A"8 end

solution.rb1 solve :two_parallel_wires, using: [MagneticFieldOfCurrents, MagneticForce] do2   objects :a, :b3 4   take current_a: a.current5   take current_b: b.current6   take separation: a.distance_from_the_wire(by: b)7   take length: a.length_in_the_field8 9   deduce_from "a 10 cm section of wire A", a.length_in_the_field => "10 cm"10 11   field = b.field_near_a_wire12   force = a.force_on_a_wire13 14   answer force:, in: "N", figures: 215 16   conclusion "Each wire creates a magnetic field at the other; the force per unit length is mu_0 I_1 I_2 / (2 pi d), and the total force is that times the length."17 end