Magnetic Field Lines: What Causes Gaps?

[abrahamjp]

Hello All,

I was just checking magnetic field lines as in attached figure.

I am curious to see some gaps between adjecent field lines in the figure.
Why it is not like a sheath( for example in lighting field) but as lines?

Thanx in advance

Abraham

 

[Nick O]

There is actually a continuum of field lines, but only a finite number of discrete lines can be visualized by this method.

Others will probably give more knowledgeable answers, but I suspect that the gaps between the lines of iron fillings are caused by magnetic forces between the fillings themselves.

 

[sophiecentaur]

Field lines are only a 'construct' to give an idea what the field is doing. There are alternative ways of showing the field. You can write pairs of numbers on a regular grid (magnitude and direction of the magnetic field vector) or you can draw contours of equal potential - but we are not familiar with that way. The spacing between the lines gives an indication of the strength of the field - close together means strong.
When you do the trick with iron filings, the tiny bits of iron actually affect the local H field strength and produce a local B field. This means they tend to stick together in chains. It's a stunning demonstration but you shouldn't read too much into what you see - or expect to get a 'measurement' out of the picture.
The 'holes' in the picture are where the field is too low for the filings to stick together.