\textbf{187.} A flat coil consisting of 50 loops with surface area of each loop $64\pi \, \text{cm}^2$ is placed in a magnetic field. If a current of 8 A passes through it, what is the magnitude of the magnetic field at the center of the coil? $\left(\mu_\circ = 4\pi \times 10^{-7} \, \dfrac{\text{T.m}}{\text{A}}\right)$
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(1) $10^{-3}$ \quad (2) $10^{-3}\pi$ \quad (3) $1.6 \times 10^{-3}$ \quad (4) $2 \times 10^{-3}\pi$
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