# A long straight wire along the Z-axis carries a current 'I' in the negative Z-direction . The induced magnetic field B at a point having coordinates (x,y) is

$\begin {array} {1 1} (1)\;\large\frac{\mu_0I(X \overline i-Y \overline j)}{2\pi( x^2+y^2)} & \quad (2)\;\large\frac{\mu_0I(X \overline j-Y \overline i)}{2\pi( x^2+y^2)} \\ (3)\;\large\frac{\mu_0I(X \overline i+Y \overline j)}{2\pi( x^2+y^2)} & \quad (4)\;\large\frac{\mu_0I(Y \overline i-X \overline j)}{2\pi( x^2+y^2)} \end {array}$

(4) $\large\frac{\mu_0I(Y \overline i-X \overline j)}{2\pi( x^2+y^2)}$