An infinitely long wire carrying current $I$ is along the $Y$-axis such that its one end is at point $A(0, b)$ while the wire extends up to $+\infty$. Find the magnitude of the magnetic field strength at point $(a, 0)$.

• A
  $\frac{{\mu _0}I}{{4\pi a}}\left( {1 + \frac{b}{{\sqrt {{a^2} + {b^2}} }}} \right)$
• B
  $\frac{{\mu _0}I}{{4\pi a}}\left( {1 - \frac{b}{{\sqrt {{a^2} + {b^2}} }}} \right)$
• C
  $\frac{{\mu _0}I}{{4\pi a}}\left( {\frac{b}{{\sqrt {{a^2} + {b^2}} }}} \right)$
• D
  None of these