Four long straight thin wires are held vertically at the corners \(A\), \(B\), \(C\) and \(D\) of a square of side \(a\), kept on a table and carry equal current \(I\). The wire at \(A\) carries current in upward direction whereas the current in the remaining wires flows in downward direction. The net magnetic field at the centre of the square will have the magnitude:
Show Hint
In square-current configurations, first calculate the field due to one wire using
\[
B=\frac{\mu_0 I}{2\pi r},
\]
then use symmetry and the right-hand thumb rule to determine the direction of the resultant magnetic field. The centre-to-corner distance of a square is always \(\frac{a}{\sqrt2}\).
