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?

Five balls numbered $1$ to $5$ are suspended using separate threads. Pairs $(1, 2)$, $(2, 4)$ and $(4, 1)$ show electrostatic attraction, while pair $(2, 3)$ and $(4, 5)$ show repulsion. Therefore ball $1$ must be

When a conducting soap bubble is negatively charged then

The charge on $500\,cc$ of water due to protons will be

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.