Question

Which wire, when current flows through it, would be surrounded by the strongest magnetic field?

A thin copper colored bar.
A copper colored coil with 2 turns.
A copper colored coil with 5 turns.
A thick copper colored bar.

Answer 1

The copper coil with 5 turns.

Reason: each loop produces a magnetic field that adds, so more turns give a stronger net field in and near the coil. For a straight conductor (thin or thick bar) the magnetic field at a given distance depends on the current (not the wire thickness), so the bars produce about the same field for the same current. Hence the 5‑turn coil produces the strongest field.