Question

What is meant by "unstable equilibrium" when theta=180 degree during the calculation of torque experienced by a dipole in an uniform electric field.

Answer 1

Dear student
$$\begin{gathered} Unstableequilibriumisthatpositionoftheelectricdipoleforwhich \\ 1)thedipolewhenslightlydisplacedfromthatpositionfurtherrotatesinthedirectionofrotationifreleasedfromthatposition. \\ 2)thepotentialenergyofthedipoleismaximum. \\ Potentialenergy \\ U=-pE\cos \theta \\ if\theta =180° \\ U=-pE\cos 180° \\ U=-pE\times (-1)=pE \\ whichisthemaximumvaluethepotentialenergyofthedipolecanassume. \\ Regards \end{gathered}$$