Answer:
the cross section refers to the way in which it is wound, in general to the circle
circle does not depend on what it has inside
Step-by-step explanation:
A solenoid is a wire wound in general in a circular shape, even when it is not forced, the cross section refers to the way in which it is wound, in general to the circle and is joined to determine the area
A = π r²
This circle does not depend on what it has inside, that is, it is the same section in the air, in a liquid or with a solid inside,