In an electromagnetic field, the lines of flux form what shape?

• A. Concentric circles
• B. Parallel lines
• C. Random lines
• D. Helical lines

Answer: (A)

Magnetic field lines around a straight current-carrying conductor form closed loops that circle the wire. These loops lie in planes perpendicular to the wire, so if you take cross-sections at different radii, you get concentric circles centered on the wire. The direction of the loops is given by the right-hand rule: with the current in a given direction, the magnetic field circles around that wire in a specific rotational sense. This is why the shape is concentric circles—every loop wraps around the wire in the same center, just at different radii. Parallel lines would imply a uniform field, random lines would lack a consistent pattern, and helical lines would require a twisting along the length, which isn’t how the field around a straight wire behaves.