JEE Main · 2026 · 21 Jan 2026 · Shift 2 · Magnetic Effects of Current

The two long straight portions lie along one line with $O$ at a perpendicular distance $r$ from it; together they form an infinite straight wire and give $B_{\text{straight}}=\frac{{\mu }_{0}I}{2\pi r}$, directed along $+\hat{i}$. The circular turn of radius $r$ produces at its centre $B_{\text{loop}}=\frac{{\mu }_{0}I}{2r}=\frac{{\mu }_{0}I}{2\pi r}\pi$, directed along $-\hat{i}$ for the current sense shown, opposing the straight-wire field. The net field is $\vec{B}=\frac{{\mu }_{0}I}{2\pi r}(1-\pi )\hat{i}=-\frac{{\mu }_{0}I}{2\pi r}(\pi -1)\hat{i}$.