\textbf{188.} A loop with radius $20\,\text{cm}$ is placed in a uniform magnetic field perpendicular to the field lines on the surface of the loop. The electrical resistance of the loop is $0.3\,\Omega$. If the magnetic field changes harmonically with time, how many tesla per second must it change so that the current in the loop is $0.2\,\text{A}$? $(\pi = 3)$
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(1) $0/2$ \hfill (2) $0/8$ \hfill (3) $2$ \hfill (4) $8$
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