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PhysicsNEET 2025Potential and potential energy of charges and dipoles

Electrostatic Potential and Capacitance

An electric dipole with dipole moment 5×10−65 \times 10^{-6} C m is aligned with the direction of a uniform electric field of magnitude 4×1054 \times 10^{5} N/C. The dipole is then rotated through an angle of 60∘60^\circ with respect to the electric field. The change in the potential energy of the dipole is:

  1. A.0.8 J
  2. B.1.0 J✓
  3. C.1.2 J
  4. D.1.5 J

Solution

U=−pEcos⁡θU = -pE\cos\theta. ΔU=−pE(cos⁡60∘−cos⁡0∘)=pE(1−12)=5×10−6×4×105×0.5=1.0\Delta U = -pE(\cos60^\circ - \cos0^\circ) = pE\left(1 - \tfrac12\right) = 5\times10^{-6} \times 4\times10^{5} \times 0.5 = 1.0 J.

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