Consider three point objects $P, Q$ and $R$. $P$ and $Q$ repel each other,while $P$ and $R$ attract. What is the nature of the force between $Q$ and $R$?

Which of the following charges is possible?
$(a)\ 3.2 \times 10^{-20} C$ $(b)\ 3.2 \times 10^{-18} C$
$(c)\ 3 \times 10^{-19} C$ $(d)\ 6 \times 10^{-17} C$

$A$ polythene piece rubbed with wool is found to have a negative charge of $3 \times 10^{-7} \;C$.
$(a)$ Estimate the number of electrons transferred (from which to which?)
$(b)$ Is there a transfer of mass from wool to polythene?

How can you represent experimentally that $(i)$ there are two types of charges and $(ii)$ there is repulsion between two like charges and attraction between two unlike charges?

From the following,what charges can be present on oil drops in Millikan's experiment? (Here $e$ is the electronic charge)

$A$ positively charged glass rod is brought near an uncharged metal sphere,which is mounted on an insulated stand. If the glass rod is removed,what is the net charge on the metal sphere?