Question

Four long parallel wires are arranged on a plane, as shown in the attached figure, with 2.0 cm gaps between them. Each wire carries a 6.0 A current in the direction indicated by the arrow. On the wire labeled B, what is the magnetic force per meter in N/m?

(1) 1.8 × 10⁻⁴ 

(2) 2.8 × 10⁻⁴ 

(3) 6.0 × 10⁻³ 

(4) 4.5 × 10⁻³ 

(5) 9.0 × 10⁻⁵

Answer 1

Correct option: (1) 1.8 × 10⁻⁴

Explanation:

We first note that wire B is repelled from both A and C, so there is no net effect from them. The only net force is with D. A quick calculation yields the value of the force per unit length as  F/L =μ_oi_Ai_c / 2πd = (π x 10^-7) x 6 x 6 / ( 2π x 0.04) = 1.8 x 10^-4 N/m.