Explain What It Means When We Say a Substance Is Magnetic

By Walter Unglaub

If we have a substance and we call it magnetic, this can describe one of two things. Find out about what it means when we say a substance is magnetic with help from an experienced physics professional in this free video clip.

Transcript

Hello, my name is Walter Unglaub, and this is, explain what it means when we say a substance is magnetic. If we have a substance and we call it magnetic, this can describe one of two things. Either the substance is a permanent magnet, or it is a ferro magnet in the sense that it can align with an external magnetic field. So what do I mean by this alignment? Well, if you think of tiny little loops of current that are traveling here in a counter-clockwise fashion, this is kind of a side view, then a magnetic field will be generated. So this interaction between electricity and magnetism is described by Maxwell's equations, and essentially if you look at an atom, which has a little nucleus and electrons orbiting around it, the atom can have a small magnetic dipole moment. And this doesn't just apply to atoms, but it can also apply to molecules for example. They can have some sort of effective dipole moment. So, this dipole moment is a vector, and if the substance is a permanent magnet, we have all the particles that constitute that substance have magnetic dipole moments that are mostly aligned in the same direction. So when we have all of these moments aligned in the same direction, the resultant or effective magnetic field will cause the substance to act like a magnet. So conventionally the magnetic field points from north to south. So, if you bring in another permanent magnet, and you have the same alignment, the same direction, then there will be an attractive force because these magnetic fields want to align. And this is one example of what we mean when we say a substance is magnetic. Another example would be if the spins inside of the substance aren't necessarily already aligned, so in that sense it's not a permanent magnet, but if we bring in an external magnetic field, and place that substance inside of it. If the spins readily align with that external magnetic field, then it will feel that presence of the magnetic field and will act as a magnet. So this is an example of a ferro magnet, but the point is describing a substance as magnetic is either due to the fact that the spins are all aligned, hence they can act like a magnet, or the spins can react very easily to an external magnetic field and be attracted to that magnet that is creating that external magnetic field. This is how you can pick up certain types of metal objects such as paper clips with a magnet. The paper clip isn't necessarily a magnet itself, but since the spins align in the presence of that magnetic field, we can call that substance magnetic. My name is Walter Unglaub and this is explain what it means when we say a substance is magnetic.