Re: [轉錄]90學年度第2學期林敏聰普物期中考
Consider a magnetic dipole μ in magnetic field B. Show that the energy
difference of the states between the maximal and minimal values is 2μB.
(10%)
A magnetic dipole in an external magnetic field has a magnetic potential
energy that depends on the dipole's orientation in the field.
We find that the potential energy U at any angle θ is
U(θ) = - μBcosθ
An magnetic dipole has its lowest energy(= -μBcos0 = -μB)
when its dipole moment is lined up with the magnetic field B.
It has its highest energy(= -μBcos180°= +μB) when vector μ
is directed opposite the field.
So the energy difference of the states between the maximal and
minimal values is U(180°) - U(0°) = +μB - (-μB) = 2μB
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