\textbf{184-} The number of rectangular loops of a coil equals the number of turns of a solenoid, and the electric current through them is equal. If the magnetic field created inside the solenoid equals the magnetic field at the center of the coil, what is the length of the solenoid in terms of the coil's diameter?
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(1) $1$ \hfill (2) $2$ \hfill (3) $\dfrac{1}{2}$ \hfill (4) $\dfrac{1}{4}$
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