Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why does magnetic force tend to increase magnetic energy?

  1. Oct 15, 2011 #1
    Hello. So: Why does magnetic force tend to increase magnetic energy?
    1) Usually, forces go in the direction of energy minimums. Why in this case is the opposite?
    2) What does it imply?

    What is that makes magnetism particular in some senses, for example this, for example its force function form?

    Thanks to everyone.
  2. jcsd
  3. Oct 15, 2011 #2

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    It doesn't. Perhaps you could explain what it is that is leading you to think otherwise.
  4. Oct 15, 2011 #3
    I could see two instances in which you would experience an increase in force:

    1) When you have a fixed source, but you are decreasing the length of the magnetic path (i.e. by bring a magnet closer to metal)
    2) When you have a fixed magnetic path (all metals parts stay in place), but you increase the field strength through adding energy to the system (i.e. increasing the current through an electromagnet).

    In case 1, you are actually losing energy in the system as you bring the magnet and metal closer together. The system is giving up energy to whatever is holding the two pieces. That is, there is a distance and force which equates to energy. Likewise, when you pull the magnet from the metal, you give up energy in your efforts, and the field gains energy.

    In case 2, yes, you are putting more energy into the feild through increase of the current.

    In a magnetic device containing a source of magnetization, a ferromagnetic material, and an air gap, the majority of the enery is typically in the air gap. Thus engineers designing inductors typically have larger air gaps in those which are designed for higher energy storage ( E=I^2 L).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook