High School Physics

Magnetic Field lines due to a Current in a Solenoid

A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. The pattern of the magnetic field lines due to a Current in a Solenoid around that solenoid is shown in Fig. 1.

magnetic field lines through and around a current carrying solenoid
Figure 1: magnetic field lines through and around a current-carrying solenoid

If we compare the pattern of the field with the magnetic field around a bar magnet then they look similar. In fact, one end of the solenoid behaves as a magnetic north pole, while the other behaves as the south pole.

The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid. That is, the field is uniform inside the solenoid.

A strong magnetic field produced inside a solenoid can be used to magnetize a piece of magnetic material, like soft iron, when placed inside the coil (Fig. 2). The magnet so formed is called an electromagnet.

Figure 2: Current-carrying solenoid coil is used to magnetize steel rod

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