Question

A neutral water molecules $\left(H_{2}O\right)$ in its vapour state has an electric dipole moment of $6\times {10}^{-30}Cm$. If the molecule is placed in an electric field of $1.5\times {10}^4{NC}^{-1}$, the maximum torque that the field can exert on it is nearly:

• A. $4.5\times {10}^{-26}Nm$
• B. $4\times {10}^{-34}Nm$
• C. $9\times {10}^{-26}Nm$
• D. $6\times {10}^{-26}Nm$

Answer 1

The correct option is C $9\times {10}^{-26}Nm$

Dipole moment of water molecule $P=6\times {10}^{-30}Cm$

External electric field applied $E=1.5\times {10}^{4}N{C}^{-1}$

Maximum torque ${\tau }_{max}=PE=6\times {10}^{-30}\times 1.5\times {10}^4=9\times {10}^{-26}$ $Nm$