# Wiring for a trolley

A worker that maintains trolleys has to twist one part of the wiring in order to tighten up the wires. He knows that a direct current that goes through wires induces magnetic field and he wants to minimize the magnetic field in the loop to avoid any side effects.

The worker can twist the wire in two ways shown in the picture bellow. If the radius of the loop is $$r$$, and the magnetic field strength at a distance $$r$$ from a straight wire was $$H_0 = 10~\mbox{A/m}$$, what is the difference between the magnetic field strength in the middle of the loop in the case a) and b) in A/m?

Details and assumptions

• Your answer should be the absolute value of the difference between the fields.
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