Question

A glass rod when rubbed with silk cloth, acquires a charge of $1.6 \times 10^{-11}$C, then the charge on silk cloth will be:
A. $-3.2 \times 10^{-11}$C
B. $-2.4 \times 10^{-13}$C
C. $-1.6 \times 10^{-13}$C
D. $-1.6 \times 10^{-11}$C

Answer 1

Hint: Glass rod acquires a positive charge due to transfer of electrons from the glass rod to the Silk cloth, which becomes negatively charged. Charge can neither be created nor be destroyed it is conserved in nature it can only transfer in integral amounts.

Complete step-by-step answer:
An atom consists of negatively charged electrons revolving around positively charged nuclei. The negative charge appears in the form of electrons and positive charge appears as protons inside the nucleus. Upon supplying very little amount of energy electrons can leave an atom, making it ionized (or positively charged). As the electron leaves the atom there is an excess of positive charge on the atom now. In our case this is what happens with the atoms in the glass rod. Some of the electrons from the glass rod got transferred from the rod to the silk cloth when they were rubbed against each other.

The conservation of charge says that charge can neither be created nor be destroyed. So, only a transfer of charge could occur. Therefore when the glass rod acquired a positive charge of $1.6 \times 10^{-11}$ C, the silk cloth must acquire a charge of $-1.6 \times 10^{-11}$ C.

Note: Option (C) and option (D) appear to have the same magnitude of charge but point should check the powers carefully. In a hurry, one might choose the wrong answer. If there was any mechanism, that would have leaked the charge, like earthing, the charge on the two bodies i.e. glass and silk would not have remained the same in that scenario. When glass and the rod are being rubbed, they acquire equal and opposite charge, when they are isolated, they continue to acquire the same charge in absence of any leak.