Electrostatics

JEE Main level, numerical answer, medium

252 of 311

Question 252 of 311

An electric dipole of dipole moment is 6.0×10−6Cm6.0\times {10}^{-6}Cm placed in a uniform electric field of 1.5×103NC−11.5\times {10}^{3}N{C}^{-1} in such a way that dipole moment is along electric field. The work done in rotating dipole by 180∘180^{\circ}in this field will be_______mJmJ.

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Answer: 18

The work done for rotating a dipole is given by the change in the potential energy. The potential energy is given by
U=−p⃗⋅E⃗U=-\vec{p}\cdot \vec{E}
W=∆U=Uf−UiW=∆U={U}_{f}-{U}_{i}
So, the work done is
W=−pEcos⁡180∘−(−pEcos⁡0∘)=2pE=2×6×10−6×1.5×103=18mJW=-pE\cos 180^{\circ}-(-pE\cos 0^{\circ})=2pE =2\times 6\times {10}^{-6}\times 1.5\times {10}^{3}=18mJ

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