Write the definition of the unit Coulomb.

The magnetic field vector source is due to ...... and the electric field scalar source is due to ......

Why do light particles like pith balls attract towards a charged rod?

When a piece of polythene is rubbed with wool,a negative charge of $4 \times 10^{-7} \ C$ is developed on the polythene. The number of electrons transferred from wool to polythene is $\left[e = 1.6 \times 10^{-19} \ C\right]$.

$(a)$ $A$ 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?

$A$ body has a charge of $-3.2 \mu C$. The number of excess electrons will be