PHYS/GEOL 406 Homework
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   Homework #10: Due Friday, April 10, by 5:00pm.


  • intro to section 7.1. Note the "magnetic force" equation (7.1) that I mentioned. This is not quite reality, but rather a model that allows you to more easily calculate magnetic things from assuming the method of the "magnetic pole strength" 'm' in Eq. (7.1).
  • I assume you're all familiar with Fig. (7.3) that indicates how ALL magnetic fields are created by moving charges, from the sub-atomic level to the universal level (yes, there are magnetic fields throughout the universe--Earth is a seriously tiny speck in the bigger picture).
  1. All magnetic fields are created by moving charges. (You must never forget this!) You have a long straight wire that is oriented east-west. This wire has a current of 14.0A running from east to west through it. The horizontal component of Earth's magnetic field at the location of the wire points north and has a magnitude of 24,500nT.
    1. At what distance from the wire is the magnetic field strength due to the current the same as the horizontal component of Earth's field?
    2. Does cancellation of Earth's horizontal field occur above or below the wire? Explain. Hint: I like pictures.
  2. You are on Earth at a magnetic co-latitude of 23.5°. Find
    1. the horizontal component of Earth's main dipole field,
    2. the vertical component of Earth's dipole field,
    3. the total intensity of Earth's dipole field.
  3. problem 7.1
  4. You measure the vertical component of a magnetic anomaly of 47.0nT at a height of 1.20m above the surface. You raise your magnetometer up an additional 0.70m and now measure 36.5nT for the vertical anomaly. Assuming the usual magnetic dipole for this anomaly, at what distance below the surface is this item located?

That's all for homework #10.