Q117 / 180 · NEET 2013 (Karnataka) · Physics

An electric dipole of dipole moment $p$ is aligned parallel to a uniform electric field $E$. The energy required to rotate the dipole by $90^{\circ}$ is:

  • A
    $p^2 E$
  • Correct answer
    B
    $p E$
  • C
    infinity
  • D
    $p E^3$

Solution

Potential energy of dipole $$ \begin{aligned} & U=-p E \\ & \left(\cos \theta_2-\cos \theta_1\right) \\ & \text { Here } \quad \theta_2=0^{\circ} \\ & =-p E \\ & (\cos 90-\cos \theta) \\ & \theta_2=90^{\circ} \\ & \stackrel{L}{U}=P E \\ & \end{aligned} $$

Hence, the correct answer is option: 'B'.

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