Torque, P E sin$$\Theta= 2 Q l sin\Theta$$

Where,

Q is the charge

E is the electric field

l is the length of the dipole

Potential energy, U = $$-P E cos\Theta = – 2 Ql cos \Theta$$ $$\frac{\tau}{U} = \frac{2Qlsin\Theta}{-2Qlsin\Theta}$$ $$\Rightarrow -tan\Theta$$ $$\frac{\tau}{U} = -tan\Theta$$ $$U = – \frac{\tau}{-tan 60^{\circ}}$$ $$\Rightarrow \frac{8\sqrt{3}}{\sqrt{3}}$$ $$\Rightarrow -8 joule.$$

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