Magnetic field and field lines

Oersted’s Experiment

(Relation between electricity and magnetism)

The first evidence of any connection between Electricity and magnetism was established by Hans Christian Oersted. He accidentally discovered that as he laid a wire carrying an electric current near a magnetic compass needle, it got deflected as if acted upon by a magnet.

This observation led to the discovery that when current passes through a conductor, magnetic field is produced around it.

Magnetic field

The space around a magnet or a current carrying conductor, in which the force of attraction or repulsion can be experienced, is called a magnetic field.

Demonstration of magnetic field lines (Iron-filings pattern)

1.  Take a bar magnet and placed it on a cardboard.

2.  Sprinkle some iron-fillings around the magnet.

3.  Tap the cardboard gently.

4.  Iron fillings arrange themselves in a pattern as shown in figure.

Conclusion: This pattern demonstrates that under the influence of magnetic field, the fillings align themselves along the magnetic field lines.

Tracing of magnetic field lines of a bar magnet

1.   Place a bar magnet on a sheet of paper.

2.   Bring the compass near the north pole of the magnet.

3.   The needle will deflect such that its south pole points towards North Pole of the bar magnet.

4.   Mark the position of two ends of needle.

5.   Move the compass so that its south end occupies the position previously occupied by the north end.

6.   Again mark the new position of ends of needle.

7.   Repeat step 5 and 6 till you reach the south pole of the magnet.

8.   Join the points marked to get a smooth curve, which represents a field line.

Magnetic field lines

Magnetic field lines are the imaginary lines used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. The direction of the magnetic field at a point is given by the direction that a north pole placed at that point would take.

Properties of Magnetic field lines

1.   Outside the bar magnet, the magnetic field lines originate from the north pole of a magnet and end at its south pole.

2.   Inside the bar magnet, field lines move from South Pole of the magnet to the North Pole.

3.   Magnetic field lines always form closed curves.

4.   The regions, where field lines are closer, the field is strong and the regions, where the field lines are farther apart, the field is weak.

5.   The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it.

6.   The magnetic field lines never cut each other. In case, two field lines intersect each other at a point, then it will mean that at the point of intersection, the magnetic needle would point in two different directions, which is not possible.