A closely wound, circular coil with radius $2.80 \mathrm{~cm}$ has 830 turns. (a) What must the current in the coil be if the magnetic field at the center of the coil is $0.0600 \mathrm{~T} ?$ (b) At what distance $x$ from the center of the coil, on the axis of the coil, is the magnetic field half its value at
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