Magnetization by Coil

The magnetic field around a straight wire is not very strong. A strong field can be made by coiling the wire around a piece of soft iron. This electromagnet is sometimes called a solenoid. Magnetic field around a current carrying solenoid is similar to that of a bar magnet. Solenoid is a coil of a number of turns of insulated copper wire closely wrapped in a shape of a cylinder. One end of the solenoid

behaves like a magnetic North Pole and the other end behaves like the South Pole. Magnetic field lines inside the solenoid are parallel and straight. This means that the field is same at all the points inside the solenoid. When soft iron rod is placed inside the solenoid, it behaves like an electromagnet. The use of soft iron as the core of solenoid produces the strongest magnetism. We can also put

a steel bar inside the solenoid. Steel forms a permanent magnet - if steel was used inside the coil, it would continue as a magnet after the electricity was switched off. Therefore, it would not be useful as an electromagnet. Instead, permanent magnets are needed for electric motors, generators, loudspeakers and microphones.