A neutral water molecule `(H_2 O)` in its vapour state has an electric dipole moment of magnitude `6.2 xx 10^-30 cm`.
a. How far apart are the molecules' centers of positive and negative charge ?
b. If a molecule is placed in an electric field of `1.5 xx 10^4 NC^-1`, what maximum torque can the field exert on it ? (Such a field can easily be set up in the laboratory).
c. How much work must an external agent do to turn this molecule end for end in this field, starting from its fully aligned position, for which `theta = 0` ?

Explanation

a. As `p = 2 l xx q`
`l = P/(2 q) = (6.2 xx 10^-30)/(2 q)`
b. `tau_(max) = p E = 6.2 xx 10^-30 xx 1.5 xx 10^4 = 9.3 xx 10^-26 Nm`
c. `W = 2 p E = 2 xx 9.3 xx 10^-26 = 1.86 xx 10^-25 J`.