How can the magnetic field of an electromagnet be judged?

How can the magnetic field of an electromagnet be judged?

The direction of the magnetic field of the electromagnet can be judged by Ampere's rule.

Ampere rule is the rule of the relationship between the direction of the magnetic induction line excited by the current and the current, or the right-hand screw rule.

(1) the Ampere rule in the direct wire (Ampere rule 1): hold the direct wire with the right hand, let the thumb point to the direction of the current, and the four point to the direction of the magnetic line of force around the direct wire.
(2) the Ampere rule in the electric solenoid (Ampere rule two): holding the electric solenoid with the right hand to make the four fingers bending with the current direction, then the one end of the thumb is the N pole of the electrified solenoid.

The Ampere rule of a linear current is also applicable to a small straight line current. The annular current can be seen as a number of small segments of the linear current, and the direction of the magnetic intensity on the central axis of the circular current is determined by the Ampere rule of the linear current in each small section. The direction of the magnetic induction line on the central axis of the annular current is obtained by superposition. The Ampere rule of the linear current is basic. The Ampere rule of the circular current can be derived from the Ampere rule of the straight line current by the Ampere rule of the linear current, which is also applicable to the magnetic field produced by the linear motion of the charge, when the direction of the current is the same as the positive charge movement direction, and the opposite direction of the negative charge motion direction.