A current carrying circular loop of radius ' $R$ ' and current carrying long straight wire are placed in the same plane. $I_c$ and $I_w$ are the currents through circular loop and long straight wire respectively. The perpendicular distance between centre of the circular loop and wire is ' $d$ '. The magnetic field at the centre of the loop will be zero when separation ' $d$ ' is equal to

• Correct answer
  A

  $\frac{R I_w}{\pi I_c}$
• B

  $\frac{R I_{\mathrm{e}}}{\pi \mathrm{I}_{\mathrm{w}}}$
• C

  $\frac{\pi \mathrm{I}_{\mathrm{c}}}{\mathrm{RI}_{\mathrm{w}}}$
• D

  $\frac{\pi \mathrm{I}_{\mathrm{w}}}{\mathrm{R}_{\mathrm{c}}}$

Hence, the correct answer is option: 'A'.