What is called quantization of electric charge ? Write $SI$ unit of electric charge.

Which is the instrument to detect the charge on the body ? Explain it with diagram.

Which scientist represented the types of charges ?

A charged metallic sphere $A$ is suspended by a riylon thread. Another charged metallic sphere $B$ held by an insulating handle is brought close to $A$ such that the distance between their centres is $10 \,cm ,$ as shown in Figure $(a) .$ The resulting repulsion of $A$ is noted (for example, by shining a beam of light and measuring the deflection of its shadow on a screen). Spheres $A$ and $B$ are touched by uncharged spheres $C$ and $D$ respectively. as shown in Figure $(b)$ $C$ and $D$ are then removed and $B$ is brought closer to $A$ to a distance of $5.0 \,cm$ between their centres, as shown in Figure $(c)$ What is the expected repulsion of A on the basis of Coulomb's law? Spheres $A$ and $C$ and spheres $B$ and $D$ have identical sizes. Ignore the sizes of $A$ and $B$ in comparison to the separation between their centres.

What is earthing or grounding in household electrical circuit ?

When the charge is considered as point ?