AIIMS 2019 Physics Magnetic Field due to Current MCQ Question

To determine the distance from a long straight wire carrying a current (I) where the magnetic field (B) is equal to 3×10⁻⁵ Wb/m², we use the formula for the magnetic field around a straight conductor: $B = \frac{{\mu_0 I}}{{2\pi r}}$, where $\mu_0$ is the permeability of free space (4π × 10⁻⁷ T·m/A). Rearranging the formula to solve for r gives $r = \frac{{\mu_0 I}}{{2\pi B}}$. Substituting $I = 12 \, \text{A}$ and $B = 3 \times 10^{-5} \, \text{Wb/m}^2$ results in $r = 6 \times 10^{-2} \, \text{m}$, confirming option A as correct.

Options B, C, and D yield distances of 12×10⁻² m, 18×10⁻² m, and 24×10⁻² m, respectively, which do not satisfy the equation derived from the magnetic field formula, indicating they are incorrect. Understanding the relationship between current, distance, and magnetic field strength is crucial in electromagnetism.