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Q.Derive an expression for potential energy of electric-di-pole placed in an uniform electric field.

Karnataka PUCKarnataka II PUC Board 2019Subjective· 3mImportance★★★★★
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The potential energy of a dipole in a uniform field is U=−pEcos⁡θ=−p⃗⋅E⃗U = -pE\cos\theta = -\vec{p}\cdot\vec{E}, derived from the work done against the aligning torque.

Concept. A dipole of moment pp in a uniform field EE experiences a torque τ=pEsin⁡θ\tau = pE\sin\theta that tends to align it with the field. Rotating the dipole against this torque stores potential energy.

Derivation. The work done in rotating the dipole through a small angle dθd\theta against the torque is

dW=τ dθ=pEsin⁡θ dθ.dW = \tau\, d\theta = pE\sin\theta\, d\theta.

Taking the reference position at θ0=90∘\theta_0 = 90^\circ (where U=0U = 0), the potential energy at angle θ\theta is …

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