The direction of the magnetic field of an electromagnet can be determined by the Ampere rule.

(1) the Ampere rule in the direct current wire (Ampere rule one): hold the straight wire through the right magnet factory, let the thumb point to the current direction, and the four refers to the direction of the magnetic line of the direct current conducting wire.

(2) the Ampere rule in the electric solenoid (Ampere rule two): holding the electric solenoid with the right hand so that the four finger bends in accordance with the direction of the current, then the end of the thumb refers to the N pole of the energized solenoid.

Electromagnet:

The magnetic effect of current, the soft iron magnetic device.

(1) the soft iron bar into a spiral coil, when the coil with current coil, the internal magnetic field of the soft magnet magnetizing iron temporarily, but the current is cut off, then the magnetic coil and soft iron vanish.

(2) the magnetic field generated by the magnetized iron rods, plus the original coil in the magnetic field, the magnetic field strength is greatly enhanced, so the magnetic solenoid is greater than that of the natural magnet.

(3) the larger the coil current is, the more the coil turns, and the stronger the magnet's magnetic field is.