If electromagnetic radiation represents a transfer of energy, then doesn't a permanent magnet represent unlimited energy, and if so, why can't magnets be used for perpetual motion? Even if permanent magnets aren't permanent and rather just have a really long usable lifetime, don't they at least represent a large resource of energy?
A (non-accelerated) permanent magnet doesn't produce electromagnetic radiation. It is surrounded by a magnetic field (just like a charge is surrounded by an electric field), but it does not radiate. Especially there's no energy leaving the magnet.
Note that for energy flow (as in radiation) you need both an electric and magnetic field, because only then you'll get a non-vanishing Pointing vector $\vec S=\vec E\times\vec B$. However note that even if you have energy flow, you don't necessarily have radiation (e.g. if you have a constantly moving charge, the field energy is flowing with the charge, but it doesn't radiate).
An object has potential energy if it has the capacity to do work. Work is done if an object is moved by a force in the direction of the said force. A permanent magnet can via it's force fields move a ferromagnetic material. Energy is said to be transfered whenever work is done. Permanent magnets emit force fields which are identical to the force fields that are emited from electromagnets. Permanent magnets can do work on an object that can be measured (force X distance). Correction with ref: celtschk with thanks.
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protected by Qmechanic♦ Dec 19 '12 at 12:55
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