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 P: 208 Hello, I have this problem. I calculated the dipole energy of a dipole moment in an external field using the equation $U_m=\frac{1}{2}\int\vec{A}\vec{J}dr^3=\frac{1}{2} \vec{\mu}.\vec{B}$ however when the force on a dipole is calculated using $\int\vec{J}\times\vec{B}dr^3$ the formula obteined for the energy is $-\vec{\mu}.\vec{B}$ I don't understand the difference, are they supposed to be defferent?