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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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1925 Upvotes
Verified Answer
The correct answer is:
$p E$
Potential energy of dipole
$$
\begin{aligned}
& U=-p E \\
& \left(\cos \theta_2-\cos \theta_1\right) \\
& \text { Here } \quad \theta_2=0^{\circ} \\
& =-p E \\
& (\cos 90-\cos \theta) \\
& \theta_2=90^{\circ} \\
& \stackrel{L}{U}=P E \\
&
\end{aligned}
$$
$$
\begin{aligned}
& U=-p E \\
& \left(\cos \theta_2-\cos \theta_1\right) \\
& \text { Here } \quad \theta_2=0^{\circ} \\
& =-p E \\
& (\cos 90-\cos \theta) \\
& \theta_2=90^{\circ} \\
& \stackrel{L}{U}=P E \\
&
\end{aligned}
$$
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