What Are Neutral Points?

What Are Neutral Points?

A neutral point is a point at which the resultant magnetic field is zero. In general, the neutral point is obtained when the horizontal component of earth’s field is balanced by the field produced by the magnet. So let us see where the neutral point will be in various different cases.

Mapping Of Magnetic Field Lines Of Earth And A Bar Magnet

Now let’s consider the case that the north pole of a bar magnet is facing the geographical north. If we take the directions in a compass, east, west north and south, then earth’s magnetic field lines extend from geographical south to geographical north. These lines will be marked upwards, from geographical south to geographical north. If we keep a compass on the line then the north pole of the compass will point in the same direction of the line, that is upwards or the geographical north. Therefore, the lines go from the geographical south to the geographical north.

Now if we want to draw the magnetic field lines of a bar magnet, then basically you take the bar magnet and place it down, now you bring a compass and fix the south pole of the compass needle to the north of the bar magnet. Now the geographical north that is shown in the compass needle is where you put your first point, just right in front. Now you move the compass needle front and put another mark, continue this and mark the points at different points around the bar magnet, you will eventually reach the south. Now when you connect these points you get the mapping of the magnetic field lines., this is purely for the bar magnet. The lines are directed from the north to the south pole of the bar magnet. If you take it in the opposite direction, the result will be the same but mirrored, again from the north pole of the bar magnet to the south pole. Similarly, we can take the magnetic field lines that are even closer to the bar magnet, the resulting line will appear below our original line but in the same form and the same direction, directed from the magnetic north to the magnetic south. Same on the opposite side.

Now if we combine the earth’s magnetic field lines and the bar magnet’s magnetic field lines, what we want to do is draw the magnetic field lines of the bar magnet in the magnetic field of the earth, with the north pole of the bar magnet facing the geographical north pole, then the magnetic field lines look different.

Now consider the above given bar magnet with all its magnetic field lines drawn around it from north to the south. Now because this is the earth’s magnetic field, there is a geographical north and a geographical south. Now the lines from the bar magnet extend on each of the geographical ends, the lines in the north of the bar magnet extend to the geographical north since there is a magnetic south, but in case of the south the earth magnetic lines will extend to the south pole of the bar magnet. The earth’s magnetic field lines hence, extend from the south pole towards the north pole or from the magnetic north to the magnetic south.

Now there are points between the magnetic field lines of the earth and the magnetic field lines of the bar magnet, where they intersect and cancel out each other. These are called the neutral points. Now what happens if we flip our experiment and try it from the south pole of the bar magnet facing the geographical north. What happens, as a whole is, the earth’s magnetic field lines move from south to north and the bar magnet’s magnetic field lines move from north to south. When we combine these two in the magnetic field of earth the lines look different, they curve around the magnet. So, the neutral points will appear again where the magnetic field of earth of the earth and the magnetic field of the bar magnet cancel each other, only this time they will along the axis of the bar magnet.

In Summary

So, any point in the magnetic field around a bar magnet, at which the resulting field intensity is zero is called a neutral point. When a bar magnet is placed flat on a horizontal table, the magnetic field around the magnet is the resultant of the field of the magnet and horizontal component of earth’s magnetic field. It is also important to know that the field intensity goes from stronger to weaker the more we move away from the poles. The earth’s horizontal component is constant. The horizontal component of the earth’s magnetic field and a bar magnet’s field intensity are exactly equal but opposite. Hence, the resultant field intensity at these intersecting points is zero.

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