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Children and mini-magnets: comments and suggestions
  1. L Finegold
  1. Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA;

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    I read with interest “Children and mini-magnets”1 for I had previously listed similar events.2 The authors illustrate the difficulty of separating attracted magnets when avoiding further trauma to the entrapped tissue, as the usual methods—of sliding the magnets apart, or using standard instruments—cannot be used. It is possible to “short out” the effective strength of a magnet (in the same way that the soft iron keeper of a horseshoe magnet greatly diminishes its external attraction) by putting a high permeability material between the poles. One such material is “Permalloy”, and pieces and sheet can be formed around a magnet. (McCormick et al do not seem to list the magnetisation directions in the shape they encountered, so one cannot make any more specific suggestions.) Permalloy might be available in your friendly neighbourhood physics department. Another technique is to put a third similar magnet against one of the two problem ones.

    Here in the USA, powerful magnets are used to hold ear “rings” or ear studs in place. A friend, who has given magnetic jewelled studs as science encouragement to pre-teen girls, has received thanks from their mothers: the mothers emphatically prefer the magnets to pierced ears.

    I am curious about the origin of the Sheffield magnets: extremely powerful ones are found in discarded computer hard drives, but they have irregular shapes.