If a charge on the body is $1 \ nC$,then how many electrons are present on the body?

$A$ 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?

Which experiment was used to determine the quantization of electric charge?

Discuss the method of charging two spheres without contact.

When is a charge considered a point charge?

$(a)$ $A$ comb run through one's dry hair attracts small bits of paper. Why? What happens if the hair is wet or if it is a rainy day? (Remember,a paper does not conduct electricity.)
$(b)$ Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary?
$(c)$ Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why?
$(d)$ $A$ bird perches on a bare high power line,and nothing happens to the bird. $A$ man standing on the ground touches the same line and gets a fatal shock. Why?