| Both sides previous revision Previous revision Next revision | Previous revision Next revisionBoth sides next revision |
| 184_notes:perm_mag [2021/06/10 03:28] – [Magnetic Field from a Bar Magnet] bartonmo | 184_notes:perm_mag [2021/06/16 18:48] – [Magnetic Field from a Bar Magnet] bartonmo |
|---|
| ===== Non-Magnetic Materials ===== | ===== Non-Magnetic Materials ===== |
| [{{ 184_notes:Week9_9.png?200|Randomized magnetic fields sum to a net magnetic field of zero}}] | [{{ 184_notes:Week9_9.png?200|Randomized magnetic fields sum to a net magnetic field of zero}}] |
| If every atom has a magnetic field from its moving charges, why is //everything// not a magnet? For a non-magnetic material (like plastic, wood, glass, etc.) the direction of the magnetic field for every atom is randomized (shown in the figure). When you take the add up the magnetic field vectors from all the atoms in the material, you get a net magnetic field of zero. | If every atom has a magnetic field from its moving charges, why is //everything// not a magnet? For a non-magnetic material (like plastic, wood, glass, etc.) the direction of the magnetic field for every atom is randomized (shown in the figure to the right). When you take the add up the magnetic field vectors from all the atoms in the material, you get a net magnetic field of zero. |
| |
| ===== Permanent Magnets ===== | ===== Permanent Magnets ===== |
| [{{184_notes:Week9_10.png?200|Magnetic fields from atoms point in the same direction in permanent magnets }}] | [{{184_notes:Week9_10.png?200|Magnetic fields from atoms point in the same direction in permanent magnets }}] |
| In contrast to non-magnetic materials, permanent magnets (also called [[https://en.wikipedia.org/wiki/Ferromagnetism|ferromagnets]]) are materials where the magnetic fields from all the atoms point in (roughly) the same direction. This is usually accomplished by putting the material in a very strong magnetic field (typically from a large current rather than another ferromagnet). It is possible for the field from each of the atoms to start to randomize (or un-align themselves) but this generally takes a very long time for a permanent magnet. (There are also other kinds of magnetic materials besides ferromagnets, such as [[https://en.wikipedia.org/wiki/Diamagnetism|diamagnets]], [[https://en.wikipedia.org/wiki/Paramagnetism|paramagnets]], and [[https://en.wikipedia.org/wiki/Antiferromagnetism|antiferromagnets]] - but we won't talk about those in this class.) | In contrast to non-magnetic materials, permanent magnets (also called [[https://en.wikipedia.org/wiki/Ferromagnetism|ferromagnets]]) are materials where the magnetic fields from all the atoms point in (roughly) the same direction (seen in the figure above). This is usually accomplished by putting the material in a very strong magnetic field (typically from a large current rather than another ferromagnet). It is possible for the field from each of the atoms to start to randomize (or un-align themselves) but this generally takes a very long time for a permanent magnet. (There are also other kinds of magnetic materials besides ferromagnets, such as [[https://en.wikipedia.org/wiki/Diamagnetism|diamagnets]], [[https://en.wikipedia.org/wiki/Paramagnetism|paramagnets]], and [[https://en.wikipedia.org/wiki/Antiferromagnetism|antiferromagnets]] - but we won't talk about those in this class.) |
| |
| ===== Induced Magnets ===== | ===== Induced Magnets ===== |
| |
| [{{ 184_notes:Week9_12.png?400|Magnetic vector field about a permanent bar magnet}}] | [{{ 184_notes:Week9_12.png?400|Magnetic vector field about a permanent bar magnet}}] |
| Since the magnetic field is a vector field, it has both a magnitude and a direction at every location in space, which we can represent with an arrow at various points around the magnet. Closer to the poles of the magnet, the field is much stronger, which we represent with longer arrows. By convention, we say that the direction of the magnetic field points away from the north pole and in towards the south pole outside of the magnet (note that the magnetic fields from the atoms inside the magnet point from the south pole to the north pole). So in lieu of carrying iron filings around with us, we represent the magnetic field of bar magnet as shown in the figure. (You may notice that these magnetic field lines look very similar to those of an [[184_notes:pc_force|electric dipole]].) | Since the magnetic field is a vector field, //it has both a magnitude and a direction at every location in space//, which we can represent with an arrow at various points around the magnet. Closer to the poles of the magnet, the field is much stronger, which we represent with longer arrows. By convention, we say that the direction of the magnetic field points away from the north pole and in towards the south pole outside of the magnet (note that the magnetic fields from the atoms inside the magnet point from the south pole to the north pole). So in lieu of carrying iron filings around with us, we represent the magnetic field of bar magnet as shown in the figure. (You may notice that these magnetic field lines look very similar to those of an [[184_notes:pc_force|electric dipole]].) |
| |
| ===== Measuring Earth's Magnetic Field and other Magnetic Fields ===== | ===== Measuring Earth's Magnetic Field and other Magnetic Fields ===== |