We’ve all done the experiment. The teacher brings out a dusty box of permanent bar magnets and everyone spends the rest of the lesson sprinkling iron filings over their desk, or worse, taking countless reading from a compass.
And what have we learnt after these shenanigans? That magnetic field lines have a “butterfly’s wings” shape, field lines emerging from the magnet’s north pole and travelling in a wide arc before terminating at the south. The lines show the route that a–theoretical–magnetic monopole would follow when placed at any point in the field. This is exactly akin to how electric field lines show the path that a positively charged particle would follow. Since monopoles have never been witnessed, the nearest we get to this is using iron filings, which respond to the magnetic field and orient themselves along the direction of the lines, one of their ends a “south” pole, the other a “north”.
All well and good, but I think the pictures of solar flares on the surface of the sun illustrate the concept of magnetic field lines a tad more dramatically than bar magnets and iron filings. The curved line are streams of plasma–matter stripped of electrons–and are highly charged. Charged particles in a magnetic field will experience a force perpendicular to both the field lines and the its own velocity; hence the curved “inward” path of the plasma. Note that the plasma doesn’t trace the path of the field lines–those lines are theoretical constructs and exist at right-angles to the plasma.
What’s coolest is that these streams of charged particles themselves cause other magnetic fields which interact with the original fields. When lines get too tangled, like a short circuit, they can snap and reconnect. When this happens they release vast quantities of energy in the form of a solar flare. An event that can chaos to electrical systems on Earth if the flare heads towards us!
The above image was captured with NASA’s Solar Dynamics Observatory in the far UV range of the spectrum. You can play with more images at this and other wavelengths at helioviewer.org.
Can you predict when the next magnetic storm might hit Earth?
Image Credit: NASA/SDO/helioviewer.org