A molecule of a substance has permanent dipole moment $p$. A mole of this substance is polarised by applying a strong electrostatic field $E$. The direction of the field is suddenly changed by an angle of $60^{\circ} .$ If $N$ is the Avogadro's number the amount of work done by the field is
  • A$\frac{1}{2}NpE$
  • B$NpE$
  • C$\;\frac{3}{2}NpE$
  • D$2NpE$
NEET 2017, Medium
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