We can define a vector called the dipole moment(电矩) NOTE: This p has q)→(+q nothing to do with momentum! Magnitude: qc Direction: from the negative(-)charge to the positive(+)charge
-q +q d p We can define a vector called the dipole moment (电矩). Magnitude: Direction: from the negative (-) charge to the positive (+) charge. p = qd NOTE: This p has nothing to do with momentum!
E,≈ Using superposition 4兀 = g +a Di pole axis P 94丌Er
3 0 4 1 r p E ⊥ − 3 0 axis 2 4 1 r p E p Using superposition…
Electric forces on dipoles →十 E p F In a uniform field, the net force on a dipole is zero: F+F=0
E - + p F+ F− In a uniform field, the net force on a dipole is zero: + = 0 F+ F− Electric forces on dipoles
Electric forces on dipoles →十 E p F But the net torque around the dipole's CoM is not zero: T=PXE
E - + p F+ F− But the net torque around the dipole’s COM is not zero: p E = Electric forces on dipoles
Electric forces on dipoles E p F This torque will rotate the dipole until it is parallel With the field
E p F+ F− This torque will rotate the dipole until it is parallel with the field. Electric forces on dipoles