What shape do the magnetic field lines form around a straight current-carrying conductor?

What shape do the magnetic field lines form around a straight current-carrying conductor?

• A. Concentric circles
• B. Parallel lines
• C. Radial spokes
• D. Helical lines

Answer: (A)

Magnetic fields around a straight current-carrying conductor form azimuthal loops that wrap around the wire. In practice, the field lines lie in planes perpendicular to the wire and are circles centered on the wire, so they are concentric circles. The direction around the wire is given by the right-hand rule: point the thumb in the direction of the current, and the fingers show the direction of the field. This circular pattern contrasts with parallel lines (which would imply a uniform field), radial spokes (which describe electric field patterns from a point source), or helical lines (which would require a component of the field along the wire). The magnetic field from a straight wire is purely tangential and circles the wire, making concentric circles the correct description.

Magnetic fields around a straight current-carrying conductor form azimuthal loops that wrap around the wire. In practice, the field lines lie in planes perpendicular to the wire and are circles centered on the wire, so they are concentric circles. The direction around the wire is given by the right-hand rule: point the thumb in the direction of the current, and the fingers show the direction of the field.

This circular pattern contrasts with parallel lines (which would imply a uniform field), radial spokes (which describe electric field patterns from a point source), or helical lines (which would require a component of the field along the wire). The magnetic field from a straight wire is purely tangential and circles the wire, making concentric circles the correct description.