Two charges of each magnitude 0 . 01   C and separated by a distance of 0 . 4   mm constitute an…

The formula to calculate the dipole moment is given by

$\left|\stackrel{\rightharpoonup }{p}\right|=q\left|\stackrel{\rightharpoonup }{d}\right| ...\left(1\right)$

Substitute the values of the known parameters into equation (1) to calculate the dipole moment.

$\begin{array}{rcl}\left|\stackrel{\rightharpoonup }{p}\right|& =& 0.01 \mathrm{C}\times 0.4 \mathrm{mm}\times \frac{1 \mathrm{m}}{{10}^3 \mathrm{mm}}\\ & =& 4.0\times {10}^{-6} \mathrm{C}·\mathrm{m}\end{array}$

The formula to calculate the torque on the dipole in the electric field is given by

$\left|\overrightarrow{\tau }\right|=|\overrightarrow{p}\times \overrightarrow{E}| ...\left(2\right)$

Substitute the values of the known parameters into equation (2) to calculate the required torque.

$\begin{array}{rcl}\left|\stackrel{\rightharpoonup }{\tau }\right|& =& 4.0\times {10}^{-6} \mathrm{C}·\mathrm{m}\times 10 \mathrm{dyne}·{\mathrm{C}}^{-1}\times \frac{1 \mathrm{N}}{{10}^5 \mathrm{dyne}}\times \sin 30°\\ & =& 2\times {10}^{-10} \mathrm{N} \mathrm{m}\end{array}$