Basic examples should include: 1, calculation result of magnetic field intensity at the center of charged ring B 1=μ0*I/(2R), 2, calculation result of magnetic field intensity at any point outside infinite conductor B2=μ0*I/(2πR).

In this topic, the arc is 3/4 of the whole circle, and the upper and lower wires are half of the infinite wires, but the extension line of the upper wire passes through the center of the circle, so it has no contribution to the magnetic field of the center of the circle, and the magnetic field direction of the center of the circle is the same as that of the next wire (right-handed rule). Therefore, generally speaking, the total magnetic field of these three segments of the center of the circle is B = (3/4) * B65438+.