Question

Two parallel, long wires are kept 0.20 m apart in vacuum, each carrying current of x A in the same direction. If the force of attraction per meter of each wire is 2 × 10-6 N, then the value of x is approximately:

• A. 1
• B. 2.4
• C. 1.4
• D. 2

Answer 1

Answer: (C)

1.4

Answer 2

The correct answer is (C) : 1.4
$\frac{dF}{dl}=2×10^{−6} N/m=\frac{μ_0i_1i_2}{2πd}$
$2×10^{−6}=\frac{2×10^{−7}×x^2}{0.2}$
$x=\sqrt2≃1.4$