Practice portal › Electric Charge and Properties › Electric Dipole
Asked in GSEB Board July 2021 · Torque, energy and work done
Idea: a dipole is +q and -q a distance 2a apart. In a uniform field both charges feel forces of the same size qE, in opposite directions.
Net force: ⃗F=q⃗E+(-q)⃗E=0
The two forces act at different points, so they form a couple. With the dipole at angle θ to the field:
τ=qE×2a sin θ=pE sin θ
This is not zero unless the dipole happens to lie along the field (θ=0° or 180°).
So F=0 and, in general, τ eq0: the dipole turns but does not drift.
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