1. The circular coil leads to the magnetic field formed by the current

(1) The magnetic field direction at the center of the coil can regard a small section of wire on the coil as a straight line, which is determined by the ampere Right-hand rule.

(2) The magnetic field generated by each small segment of current on a circular coil with a current flowing through it points in the same direction within the coil, so the magnetic field inside the coil is stronger than the magnetic field generated by a straight wire current.

(3) When a circular wire is fed with current, the magnetic field outside the coil is weaker than the magnetic field inside the coil due to the inconsistent direction of the magnetic field generated by each small current segment.

(4) The larger the current and the smaller the radius of a circular coil, the stronger the magnetic field at the center of the coil.

(5) The magnetic field lines of circular coils and circular thin magnets are similar in shape.

2. Magnetic field of spiral coil current

(1) Using a long wire to form a spiral shaped coil is equivalent to being formed by connecting multiple circular coils in series. The magnetic field established at the center of each circular wire is in the same direction, which can enhance the effect. Therefore, the magnetic field at the center of the coil is stronger than that of a single turn circular coil.

(2) The magnetic field lines inside the coil form a straight line with the same direction, while the magnetic field lines at approximately both ends of the coil gradually bend outward.

(3) The magnetic field characteristics of a spiral coil are similar to those of a bar magnet, with the magnetic field lines inside the coil facing opposite directions to the outside of the coil.

(4) The strength of the magnetic field inside the coil is proportional to the current on the coil and the number of coils per unit length.

3. The right-hand spiral rule for the direction of the magnetic field inside a spiral coil current (Ampere's theorem): Hold the coil with your right hand, point your four fingers in the direction of the current, and the direction indicated by your thumb is the direction of the magnetic field inside the coil.