Answer to Question #332007 in Electricity and Magnetism for Henry

Question

There is a lead XY of the shape of a long straight line and a doubly-rolled circular lead whose center is O with radius 0.10 m. They are in the same plane and the distance between XY and O is 0.20 m. A current of 15.7 A is flowing in lead XY to the direction shown in the figure below. Set the circle ratio is 3.14. Find the strength of the magnetic field which the straight line current builds at the center O of the circle.

Answer 1

$B=\frac{2\pi I}{\mu_0r}+\frac{2\pi I}{\mu_0 d}=4~mT.$