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Question: Answered & Verified by Expert
An electric dipole with dipole moment $4 \times 10^{-19} \mathrm{C}-\mathrm{m}$ is aligned at $30^{\circ}$ with the direction of a uniform electric field of magnitude $5 \times 10^4 \mathrm{NC}^{-1}$, the magnitude of the torque acting on the dipole is
PhysicsElectrostaticsKCETKCET 2022
Options:
  • A $\sqrt{3} \times 10^{-4} \mathrm{~N}-\mathrm{m}$
  • B $10^{-5} \mathrm{~N}-\mathrm{m}$
  • C $10 \times 10^{-3} \mathrm{~N}-\mathrm{m}$
  • D $10^{-4} \mathrm{~N}-\mathrm{m}$
Solution:
2932 Upvotes Verified Answer
The correct answer is: $10^{-4} \mathrm{~N}-\mathrm{m}$
Given, for an electric dipole, dipole moment, $p=4 \times 10^{-9} \mathrm{C}$ $\theta=30^{\circ}$
Magnitude of electric field, $E=5 \times 10^4 \mathrm{~N} / \mathrm{C}$
$\therefore$ Torque, $\tau=p E \sin \theta$
$$
=4 \times 10^{-9} \times 5 \times 10^4 \sin 30^{\circ}=10^{-4} \mathrm{~N}-\mathrm{m}
$$

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