This statement caused J. J. Thomson to formulate positive charges as distributed throughout matter in his plum pudding model. For 10 points each:
[10m] Name this statement that prohibits the existence of a fixed arrangement of magnets in stable equilibrium. It can be proven from Maxwell’s equations via the result that magnetic fields in free space do not achieve maxima.
ANSWER: Earnshaw’s theorem
[10e] This technology uses electromagnets with alternating polarity to circumvent the consequences of Earnshaw’s theorem, allowing trains to float above their tracks.
ANSWER: maglev [or magnetic levitation]
[10h] To lower energy costs, the Inductrack system for maglev uses permanent magnets in this configuration. Magnets in this configuration form a line and cycle among four orthogonal orientations in order to achieve nearly one-sided flux.
ANSWER: Halbach arrays
<David Bass, Physics>