Answer
(a) Charge on the silk is negative. As Glass rod acquire positive charge, it means it has lost electron. those electrons get transferred to silk so silk is negatively charged.
(b) Charge on the silk $-8\times10^{-10}C$
number of electrons transferred from glass rod to silk is $5\times10^{9}$
(c)Glass rod has lost the mass equal to $4.55\times10^{-21}kg$
Work Step by Step
(a) Charge on the silk is negative. As Glass rod acquire positive charge, it means it has lost electron. those electrons get transferred to silk so silk is negatively charged.
(b) the total electron lost by glass rod is gained by the silk. so if the charges of those electron is $+8\times10^{-10}C$ for glass rod. for silk total charge gain would be $-8\times10^{-10}C$.
Charge of electron $e= -1.6\times10^{-19}C$.
so $1.6\times10^{-19}C$ is equal to $1$ electron
$1C$ is equal to $\frac{1}{1.6\times10^{-19}} $electron
$8\times10^{-10}C$ is equal to $\frac{8\times10^{-10}}{1.6\times10^{-19}} $electron = $5\times10^{9}$ electrons
(c)
Glass rod lost $5\times10^{9}$ electrons
mass of electron $m_{e}=9.1\times10^{-31}kg$
so total mass= No.of electrons X mass of one electron
total mass= $5\times10^{9}\times9.1\times10^{-31}kg=4.55\times10^{-21}kg$
