A polythene piece rubbed with wool is found to have a negative charge of 3 × 10⁻⁷ C.

(a) Estimate the number of electrons transferred (from which to which?)

(b) Is there a transfer of mass from wool to polythene?

(a) When polythene is rubbed against wool, a number of electrons get transferred from wool to polythene. Hence, wool becomes positively charged and polythene becomes negatively charged. Amount of charge on the polythene piece, q = −3 × 10−7 C Amount of charge on an electron, e = −1.6 × 10−19 C Number of electrons transferred from wool to polythene = n n can be calculated using the relation, q = ne = 1.87 × 1012 Therefore, the number of electrons transferred from wool to polythene is 1.87 × 1012. (b) Yes. There is a transfer of mass taking place. This is because an electron has mass, me = 9.1 × 10−3 kg Total mass transferred to polythene from wool, m = me × n = 9.1 × 10−31 × 1.85 × 1012 = 1.706 × 10−18 kg Hence, a negligible amount of mass is transferred from wool to polythene. read less