A solenoid is a long, cylindrical coil of insulated wire. When an electric current is passed through this coil, it creates a magnetic field. The magnetic field lines inside a solenoid are nearly parallel to the axis and are closely spaced, indicating a strong and uniform magnetic field.
The magnetic field produced by a solenoid is similar to that of a bar magnet. The strength of the field can be increased by increasing the current, increasing the number of turns in the coil, or by placing a soft iron core inside it. When a soft iron core is used, it forms a powerful electromagnet.