Question

A polythene rod is rubbed with a silk cloth as shown
below.

Explain why, during the rubbing process, the silk
cloth becomes positively charged while the
polythene rod becomes negatively charged.

Answer 1

The material that gains electrons becomes negatively charged. The material that loses electrons is left with a positive charge. When a polythene rod is rubbed with a duster, the friction causes electrons to gain energy. Electrons gain enough energy to leave the atom and 'rub off' onto the polythene rod.

Answer 2

When a piece of polythene is rubbed with a cloth, it becomes charged. Electrons are 'rubbed' off the cloth and onto the polythene by friction. This makes the polythene negatively charged and leaves the cloth positively charged.