A wire carrying current I is laid in shape of a curve which is represented in plane polar co- ordinate system as `r = b + c/ pi   theta` for `0 lt theta lt pi/2` Here b and c are positive constants. `theta` is the angle measured with respect to positive x direction in anticlockwise sense and r is distance from origin (see figure). Calculate the magnetic field at the origin due to the wire.

Answer

`(mu_(0)I)/(4c) l n(1+c/(2b))odot`