Energy Stored in Magnetic Fields
Main article: Magnetic energy See also: Magnetic hysteresisEnergy is needed to generate a magnetic field both to work against the electric field that a changing magnetic field creates and to change the magnetization of any material within the magnetic field. For non-dispersive materials this same energy is released when the magnetic field is destroyed so that this energy can be modeled as being stored in the magnetic field.
For linear, non-dispersive, materials (such that B = μH where μ is frequency-independent), the energy density is:
If there are no magnetic materials around then μ can be replaced by μ0. The above equation cannot be used for nonlinear materials, though; a more general expression given below must be used.
In general, the incremental amount of work per unit volume δW needed to cause a small change of magnetic field δB is:
Once the relationship between H and B is known this equation is used to determine the work needed to reach a given magnetic state. For hysteretic materials such as ferromagnets and superconductors the work needed will also depend on how the magnetic field is created. For linear non-dispersive materials, though, the general equation leads directly to the simpler energy density equation given above.
Read more about this topic: Magnetic Field
Famous quotes containing the words energy, stored, magnetic and/or fields:
“The scholar may be sure that he writes the tougher truth for the calluses on his palms. They give firmness to the sentence. Indeed, the mind never makes a great and successful effort, without a corresponding energy of the body.”
—Henry David Thoreau (1817–1862)
“After eleven years I was composing
Love-letters again, broaching the word ‘wife’
Like a stored cask,”
—Seamus Heaney (b. 1939)
“We are in great haste to construct a magnetic telegraph from Maine to Texas; but Maine and Texas, it may be, have nothing important to communicate.”
—Henry David Thoreau (1817–1862)
“When we walk, we naturally go to the fields and woods: what would become of us, if we walked only in a garden or a mall?”
—Henry David Thoreau (1817–1862)