12.2.4 Magnetic Field due to a Current in a Solenoid

. . Magnetic Field 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 around a current-carrying solenoid is shown in Fig. . . Compare the pattern of the field with the magnetic field around a bar magnet (Fig. . ). Do they look similar? Yes, they are 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 magnetise a piece of magnetic material, like soft iron, when placed inside the coil (Fig. . ). The magnet so formed is called an electromagnet. Field lines of the magnetic field through and around a current carrying solenoid. A current-carrying solenoid coil is used to magnetise steel rod inside it – an electromagnet. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop. The magnetic field in a given region is uniform. Draw a diagram to represent it.