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Question: Answered & Verified by Expert
A sample of $\mathrm{HCl}$ gas is placed in an electric field $3 \times 10^{4} \mathrm{NC}^{-1}$. The dipole moment of each $\mathrm{HCl}$ molecule is $6 \times 10^{-30} \mathrm{~cm}$. The maximum torque that can act on a molecule is
PhysicsElectrostaticsVITEEEVITEEE 2008
Options:
  • A $2 \times 10^{-34} \mathrm{C}^{2} \mathrm{Nm}^{-1}$
  • B $2 \times 10^{-34} \mathrm{Nm}$
  • C $18 \times 10^{-26} \mathrm{Nm}$
  • D $0.5 \times 10^{34} \mathrm{C}^{-2} \mathrm{Nm}^{-1}$
Solution:
2483 Upvotes Verified Answer
The correct answer is: $18 \times 10^{-26} \mathrm{Nm}$
Here
$\begin{array}{l}
\mathrm{E}=3 \times 10^{4} \mathrm{NC}^{-1} \\
\mathrm{p}=6 \times 10^{-30} \mathrm{Cm} \\
\Gamma_{\max }=?
\end{array}$
We have,
torque acting on a dipole $\Gamma=\mathrm{pE} \sin \theta$
The maximum value of $\Gamma$, i.e. $\Gamma_{\max }=\mathrm{pE}$
$\begin{aligned}
\therefore \Gamma_{\max } &=\left(3 \times 10^{4} \times 6 \times 10^{-30}\right) \mathrm{Nm} \\
&=18 \times 10^{-26} \mathrm{Nm}
\end{aligned}$

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