1. ‘Na’ is orienting towards -ve side and cl ions towards +ve side.
2.
Consider an electric dipole of dipole moment P = 2aq kept in a uniform external electric field, inclined at an angle θ to the field direction.
torque = any one force × perpendicular distance
\(\tau\) = qE × 2 a sin θ
Since P = 2aq
\(\tau\) = p E sin θ
Vectorialy
\(\overrightarrow \tau=\overrightarrow P\times \overrightarrow E
\)
3. \(\tau\) = q2a.E
\(\tau\) = 1.6 × 10-19 × 1.3 × 10-10 × 20 Nm
= 41.6 × 10-29 Nm.