Two point charges $-4 \mu c$ and $4 \mu c$, constituting an electric dipole, are placed at $(-9,0,0) \mathrm{cm}$ and $(9,0,0) \mathrm{cm}$ in a uniform electric field of strength $10^4 \mathrm{NC}^{-1}$. The work done on the dipole in rotating it from the equilibrium through $180^{\circ}$ is :

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Aicharya · Accepted Answer

$\begin{aligned} & \mathrm{U}=-\mathrm{PE} \cos 	heta \ & \mathrm{w}_{\mathrm{ext}}=\Delta \mathrm{U}=\mathrm{U}_{\mathrm{f}}-\mathrm{U}_{\mathrm{i}}=-\mathrm{PE} \cos 180^{\circ}+\mathrm{PE} \cos 0^{\circ} \ & \mathrm{w}_{\mathrm{ext}}=2 \mathrm{PE} \ & =2 	imes\left(4 	imes 10^{-6}ight)(18) 	imes 10^4 \ & =144 	imes 10^{-2} \ & =14.4 \mathrm{~mJ}\end{aligned}$

Two point charges $-4 \mu c$ and $4 \mu c$, constituting an electric dipole, are placed at $(-9,0,0)…

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