The magnetic field intensity in college physics (acute ~ ~ ~ ~) has extra points ~ ~ ~ ~

This problem is also called infinite cable. I'll give you a hint without typing:

1. Using Ampere Loop Theorem.

2. Let the current intensity be I, and then distribute it evenly on the cross section, and distribute the current according to the area.

3.r>c is 0, because the total current in Ampere Loop Theorem is 0.

What you should pay attention to is the present.

5. The integration is simple, 2πrB=μ0I.

There should be an answer to this question online. Search in Baidu Library and enter "College Physics Test".