A long straight wire carries current I = 5 A. What is the magnetic field at r = 0.1 m? (μ0 = 4π×10^-7 T·m/A)

A long straight wire carries current I = 5 A. What is the magnetic field at r = 0.1 m? (μ0 = 4π×10^-7 T·m/A)

• A. About 1.0×10^-5 T
• B. About 1.0×10^-3 T
• C. About 1.0×10^-7 T
• D. About 1.0×10^-4 T

Answer: (A)

The magnetic field around a long straight wire is circular and its magnitude is B = μ0 I / (2π r). Plugging in I = 5 A, r = 0.1 m, and μ0 = 4π×10^-7 T·m/A gives B = (4π×10^-7 × 5) / (2π × 0.1) which simplifies to about 1.0×10^-5 T (that is, 10 μT). The field direction is tangential around the wire, determined by the right-hand rule: if the current points along the wire, curling fingers show the direction of B around it.

The magnetic field around a long straight wire is circular and its magnitude is B = μ0 I / (2π r). Plugging in I = 5 A, r = 0.1 m, and μ0 = 4π×10^-7 T·m/A gives B = (4π×10^-7 × 5) / (2π × 0.1) which simplifies to about 1.0×10^-5 T (that is, 10 μT). The field direction is tangential around the wire, determined by the right-hand rule: if the current points along the wire, curling fingers show the direction of B around it.