A current of I ampere flows in a wire forming a circular arc of radius r metres subtending an angle \[\theta \] at the centre as shown. The magnetic field at the centre O in tesla is

• A. \[\frac{{{\mu }_{0}}I\theta }{4\pi r}\]    
• B. \[\frac{{{\mu }_{0}}I\theta }{2\pi r}\]
• C. \[\frac{{{\mu }_{0}}I\theta }{2r}\]         
• D. \[\frac{{{\mu }_{0}}I\theta }{4r}\]