The working principle of an electromagnet can be summarized as a chain: current passing through a coil generates a magnetic field (current magnetic effect) → the coil concentrates the magnetic field into a tubular shape → the soft iron core is magnetized, amplifying the magnetic field hundreds or thousands of times → the magnetic circuit and air gap determine the actual output suction force. After power is cut off, the magnetic domains of the iron core return to disorder, and the magnetism disappears - this is the physical essence of the "controllability" of an electromagnet.