# A wire of length 'l' is bent into a circular loop of radius R and carries a current I. The magnetic field at the center of the loop is 'B'. The same wire is now bent into a double loop of equal radii. If both loops carry the same current I and it is in the same direction, the magnetic field at the center of the double loop will be :

$\begin {array} {1 1} (1)\;zero & \quad (2)\;2\;B \\ (3)\;4\;B & \quad (4)\;8\;B \end {array}$

(3) 4B