Consider a neutral conducting sphere. $A$ positive point charge is placed outside the sphere. The net charge on the sphere is then,

$A$ polythene piece rubbed with wool is found to have a negative charge of $3.52 \times 10^{-7} \text{ C}$. What is the number of electrons transferred?

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?

When a glass rod is rubbed with a silk cloth,charges appear on both. $A$ similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

How can an object be charged by contact?

Two identical spherical conductors $B$ and $C$ have equal radii and carry equal charges. They repel each other with a force $F$ when placed at a certain distance apart. $A$ third identical spherical conductor $A$,which is uncharged,is brought in contact with $B$ and then removed. It is then brought in contact with $C$ and removed. What is the new force of repulsion between $B$ and $C$?