Are Separated Charges

Dipoles Are Equal and Opposite Charges Separated by a Distance 

The magnitude of the force on a charge q acting in the direction of the field is qE. The force can be decomposed into two vector components fc acting in the circumferential direction to rotate the dipole, and fs acting to stretch the dipole. 

To get the work of rotating the dipole from angle 0 to 6, integrate Equation (21.17) and multiply by 2 because there is an equal torque acting on each end of the dipole  

Equation (21.18) will be useful for modelling polar molecules orienting in electric fields and gating in ion channels (see page 425). 

Displacement due to dipole orientation. The dipole of length 2a in Example 21.4 changes angle by an amount 

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