Q. A sample of $HCl$ gas is placed in an electric field of $3 \times 10^{4}\ NC^{- 1}.$ The dipole moment of each $HCl$ molecule is $6 \times 10^{- 30}c \times m.$ The maximum torque that can act on a molecule is
A) $2 \times 10^{- 34}C^{2}N^{- 1}m$
B) $2 \times 10^{- 34}Nm$
C) $18 \times 10^{- 26}\ Nm$
D) $0.5 \times 10^{34}C^{- 2}N^{- 1}m^{- 1}$
Explanation
(c) The torque on a dipole moment is $\overrightarrow{\tau} = \overrightarrow{p} \times \overrightarrow{E}.$ The maximum value is when they are perpendicular to each other so that $pE\sin\theta$ is maximum $i.e.,\sin\theta = 1$
$\tau = \left( 3 \times 10^{4}NC^{- 1} \right)\left( 6 \times 10^{- 30}c \times m \right) = 18 \times 10^{- 26}Nm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.