Electric Charges and Fields - Result Question 17

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17. 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

======= ####17. 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

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(b) $p^{2} E$

(c) $p E$

(d) infinity

[NEET Kar. 2013]

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Answer:

Correct Answer: 17. (c)

Solution:

  1. (c) When electric dipole is aligned parallel $\theta=0^{\circ}$ and the dipole is rotated by $90^{\circ}$ i.e., $\theta=90^{\circ}$.

Energy required to rotate the dipole

$\begin{aligned} W & =U_f-U_i=(-p E \cos 90^{\circ})-(-p E \cos 0^{\circ}) \\ & =p E .\end{aligned}$