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| 184_notes:perm_mag [2021/06/16 18:48] – [Magnetic Field from a Bar Magnet] bartonmo | 184_notes:perm_mag [2021/07/05 21:52] (current) – schram45 |
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| ===== Measuring Earth's Magnetic Field and other Magnetic Fields ===== | ===== Measuring Earth's Magnetic Field and other Magnetic Fields ===== |
| One of the most important magnetic fields (that we actually model as a giant bar magnet) is [[https://en.wikipedia.org/wiki/Earth%27s_magnetic_field | One of the most important magnetic fields (that we actually model as a giant bar magnet) is [[https://en.wikipedia.org/wiki/Earth%27s_magnetic_field |
| |Earth's magnetic field]]. Geophysicists believe that the source of the Earth's magnetic field are currents generated in conductive material in the Earth's core. This is particularly important when we are trying to measure a magnetic field, since all measurements are taken on Earth and will (in some way) have to include Earth's field. We have already mentioned that Earth's magnetic field is relatively small at ~$10^{-5}T$. If the magnetic field that you are measuring is large, then Earth's magnetic field may be negligible; however, if it is small, you may need to consider Earth's field more carefully in your considerations. | |Earth's magnetic field]]. Geophysicists believe that the source of the Earth's magnetic field are currents generated in conductive material in the Earth's core. This is particularly important when we are trying to measure a magnetic field, since all measurements are taken on Earth and will (in some way) have to include Earth's field. We have already mentioned that Earth's magnetic field is relatively small at ~$10^{-5}T$. If the magnetic field that you are measuring is large, then Earth's magnetic field may be negligible; however, if it is small, you may need to consider Earth's field more carefully in your assumptions. |
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| [{{ 184_notes:Week9_13.png?200|Direction of earth's magnetic field}}] | [{{ 184_notes:Week9_13.png?200|Direction of earth's magnetic field}}] |
| Since Earth's field is relatively constant, we can actually use Earth's magnetic field to measure the magnetic field from other sources. So say we have a current that runs perpendicularly to Earth's B-field (shown as out of the page/screen in the figure). If we consider a point above the wire (Point P), the Earth's magnetic field will (always) point toward the geographic north. However, the current will produce a B-field at Point P that points to the west (or $-\hat{x}$) using the right hand rule (point your fingers out of the page then curl them toward Point P - your thumb should be pointing to the left). So if we put the compass at Point P, we would expect it to point in the direction of the //**net**// magnetic field (or to the north west in this case). The example below will go into more detail about how we can use that to calculate the size of the magnetic field from the wire. | Since Earth's field is relatively constant, we can actually use Earth's magnetic field to measure the magnetic field from other sources. So say we have a current that runs perpendicularly to Earth's B-field (shown as out of the page/screen in the figure). If we consider a point above the wire (Point P), the Earth's magnetic field will (always) point toward the geographic north. However, the current will produce a B-field at Point P that points to the west (or $-\hat{x}$) using the right hand rule (point your fingers out of the page then curl them toward Point P - your thumb should be pointing to the left). So if we put the compass at Point P, we would expect it to point in the direction of the //**net**// magnetic field (or to the north west in this case). The example below will go into more detail about how we can use that to calculate the size of the magnetic field from the wire. |
| ==== Examples ==== | ==== Examples ==== |
| [[:184_notes:examples:Week9_earth_field|Using the Earth's Magnetic Field for Measurements]] | * [[:184_notes:examples:Week9_earth_field|Using the Earth's Magnetic Field for Measurements]] |
| | * Video Example: Using Earth's Magnetic Field for Measurements |
| | {{youtube>0kc-otyFZY0?large}} |