A polythene piece rubbed with wool is found to have negative charge of 3.2 x 10^-7 C. Estimate the number of electrons transferred from wool to polythene.

According to quantisation of charge, we have Q=n e, where e=1.6 x 10^-19 (the charge of electron). Therefore, the total number of electrons transferred from wool to polythene is
$\mathrm{n}=\frac{\mathrm{q}}{\mathrm{e}}=\frac{3.2\times {10}^{-7}}{1.6\times {10}^{-19}}=2\times {10}^{12}$