Question

Why is glass rod get charged when rubbed with silk cloth whereas a metallic rod not ???​

Answer 1

A glass rod has free electrons which are less tightly bound, so when the rod is rubbed with silk it loses electrons to a silk piece. The glass rod has deficiency of electrons and acquires positive charge and the rod acquires negative charge.

Iron rod being a good conductor of electricity cannot be charged by friction (rubbing) by holding it into the hand because when you charge a metal rod (iron) by friction, the rod gets extra electrons. ... Thus, the iron rod will continuously remain charge-free while holding it.

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Answer 2

The core has positive charge, the electrons have negative charge. When you are rubbing the glass rod with the silk cloth, electrons are stripped away from the atoms in the glass and transferred to the silk cloth. This leaves the glass rod with more positive than negative charge, so you get a net positive charge.