A sample of HCl gas is placed in an electric field of \( 3\times10^{4}\,\mathrm{N\,C^{-1}} \). The dipole moment of each HCl molecule is \( 6\times10^{-30}\,\mathrm{C\,m} \). The maximum torque that can act on this molecule is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 1.8\times10^{-25}\,\mathrm{N\,m} \)
The torque on an electric dipole of moment p in a uniform field E is \( \tau = pE\sin\theta \). It is largest when the dipole is perpendicular to the field, \( \theta = 90^\circ \):
\( \tau_{\max} = pE = 6\times10^{-30}\,\mathrm{C\,m}\times3\times10^{4}\,\mathrm{N\,C^{-1}} = 1.8\times10^{-25}\,\mathrm{N\,m} \)