A donut-shaped permanent magnet (magnetization parallel to the axis) can slide frictionlessly on a vertical rod. Treat the magnets as dipoles with mass $m_d$ and dipole moment $M$ . When we put two back to back magnets on the rod the upper one will float. At what height $z$ does it float?
A donut-shaped permanent magnet (magnetization parallel to the axis) can slide frictionlessly on a vertical rod. Treat the magnets as dipoles with mass $m_d$ and dipole moment $M$ . When we put two back to back magnets on the rod the upper one will float. At what height $z$ does it float?
- A
${\left[ {\frac{{2{\mu _0}{M^2}}}{{3\pi {m_d}g}}} \right]^{1/4}}$
- B
${\left[ {\frac{{6{\mu _0}{M^2}}}{{\pi {m_d}g}}} \right]^{1/4}}$
- C
${\left[ {\frac{{3{\mu _0}{M^2}}}{{2\pi {m_d}g}}} \right]^{1/4}}$
- D
${\left[ {\frac{{{\mu _0}{M^2}}}{{6\pi {m_d}g}}} \right]^{1/4}}$
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