A wire carrying current `i` has the configuration as shown in figure. Two semi-infinite straight sections, both tangent to the same circle, are connected by a circular arc of central angle theta, along the circumference of the circle, with all sections lying in the same plane. What must be for `B` to be zero at the centre of the circle?

Explanation

`2[(mu_0)/(4 pi)(i)/(R)] = (mu_0 (theta)/(2pi))/(2R) rArr theta = 2" " rad`