# When magnetic flux is in opposite directions and cancels out, forming “null points”, does that mean there is repulsion?

In some arrangements of magnets it may be hard to see if there is repulsion or attraction. For example with two bar magnets, opposite polarity, side by side, it is easy to tell that there is attraction between the poles, but if there was repulsion along the sides that would be "hidden" by net vector of attraction. In general, if magnetic flux is in opposite directions and cancels out, forming "null points", does that mean there is repulsion? If applied to image below, are the magnets, weakly, repelling one another at that null point? Or is that assumption completely wrong?

Note, this question was slightly similar to other question, has been narrowed down. Tried to ask it as precise as possible. Feel free to link to slightly related questions, or you could also provide an answer.

• It's not clear what you mean by "repelling at that null point". For example, consider a boat floating on a lake. The Earth's gravity is pulling it downward, buoyancy is pushing it upward. The Sun's gravity may be pulling it upward. The forces are distributed throughout the volume and surface of the boat. – S. McGrew May 14 '19 at 17:32
• Yes, different forces. The net force between two bar magnets, side by side, opposite polarity, is clearly attraction. Consider there may be other forces, weak, but there. The magnetic flux in between the magnets moves as it tends to do when there is repulsion, it has a null point like there tends to be when there is repulsion, and so, simple question, is there repulsive force there? – solon May 14 '19 at 17:54

It's not really appropriate to use the term "force" unless it is associated with a massive object, as in $$F = ma$$, or with something like spring compression or string tension.

In the situation you've described, the magnetic field at the "null" point is not acting on anything. If you were to measure the field strength at that point, e.g., by observing a moving charged particle there or by placing a magnetic dipole there, you would of course determine that the field strength there is zero.

The magnetic force acting on each point of either of the two bar magnets in your example depends only on the magnetic field's strength and divergence at that point of the bar magnet; it does not depend directly on the field strength or divergence anywhere else. So, it is not really meaningful to refer to attraction or repulsion at a point outside the bar magnets. Similarly, if there were a cavity inside one of the bar magnets there would be a magnetic field in the cavity, but there would be no repulsion or attraction occurring within the cavity.

There could be some misunderstanding of what's going on at that "null field" point. It kind of looks as if the field lines are repelling each other there, but that's not really what's happening. At every point in the field, the net field strength and direction is simply the vector sum of the field strength and direction of all the sources in the surrounding space. When that vector sum is mapped out, the map looks like field "lines", but the lines are not objects or even a substance like gas. They are more like lines drawn perpendicular to the contour lines in a topographic map.

• seems to be more or less consensus to use word "magnetic force", google.com/search?q=magnetic+force – solon May 14 '19 at 19:56
• Sure, it's meaningful to say that there is a "magnetic force" acting on an electron moving through a magnetic field, or on a compass needle in the Earth's magnetic field, or between two bar magnets. But "magnetic force" is not an appropriate term to use when referring to the field itself. – S. McGrew May 14 '19 at 19:59
• seems appropriate when describing force making magnets attract or repel, regardless of scale – solon May 14 '19 at 20:00
• re: a point outside the bar magnet, the rhetoric most people use seems to be that opposing magnetic flux repels. iron filings or other ways to visualize two bar magnets with like pole facing one another, show a null point, magnetic field cancelled out by opposing flux, outside the magnets, siyavula.com/read/science/grade-10/magnetism/images/… – solon May 14 '19 at 20:00
• In each case you mention, there are objects at the points being considered, such as iron filings. – S. McGrew May 14 '19 at 20:08