Question

A sample of $\text{HCl}$ gas is placed in an electric field of $2.5\times {10}^4\text{N/C}$. The dipole moment of each $\text{HCl}$ molecule is $3.4\times {10}^{-30}\text{C-m}$. Find the maximum torque that can act on a molecule.

• A. $6.5\times {10}^{-26}\text{N-m}$
• B. $7.5\times {10}^{-26}\text{N-m}$
• C. $8.5\times {10}^{-26}\text{N-m}$
• D. $9.5\times {10}^{-26}\text{N-m}$

Answer 1

The correct option is C $8.5\times {10}^{-26}\text{N-m}$

Given:
Magnitude of electric field, $E=2.5\times {10}^4\text{N/C};$

Magnitude of dipole moment, $p=3.4\times {10}^{-30}\text{cm}$

And magnitude of torque on electric dipole placed in uniform electric field is given by

$\tau =pE\sin \theta$

For maximum torque, $\sin \theta =1$

$\therefore {\tau }_{\text{max}}=pE$

$\Rightarrow {\tau }_{max}=3.4\times {10}^{-30}\times 2.5\times {10}^4$

$\Rightarrow {\tau }_{max}=8.5\times {10}^{-26}\text{N-m}$

Hence, option $\left(c\right)$ is the correct answer.