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Q & A: powerful magnets

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Most recent answer: 11/25/2011
Q:
Is there a way to make a more powerful magnet than the basic coppercoil and battery version?
- Samuel (age 16)
Murphy, NC, USA
A:
There are a variety of ways to get stronger magnetic fields. First, since batteries run down pretty quickly, a standard lab magnet will use a dc power supply driven by ac current from the power company. Second, those standard lab electromagnets include an iron core inside the copper coils. By magnetizing two big iron rods with a little gap between them, one can make the field in the gap quite large. Tapering the rods as they approach the gap makes the high-field region more intense, although smaller in diameter. These methods easily produce fields above 1T (10,000 G). (Really good permanent magnets produce fields of around 0.3T)

Larger fields can be produced using superconducting magnets. These are the types of magnets used in medical MRI facilities. These have to be kept cold. The standard ones are designed to operate at liquid helium temperatures, 4.2K, making them inconvenient for use outside a lab. (Magnets made of high-temperature superconductors can operate in liquid nitrogen, more practical for general-purpose use, but these don't reach very high fields.) A routine lab superconducting magnet can operate at say 7T, with fancier versions operating up to around 12T.  There are a variety of special techniques used in highly specialized magnet labs which can produce much higher fields briefly.

Mike W.

(published on 11/25/2011)

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