Electric field কী?

Example 14.5 (Reading a field)

A test charge $q = +2.0 \times 10^{-8}\,\mathrm{C}$ at $M$ feels a force of $6.0 \times 10^{-4}\,\mathrm{N}$ pointing east. The field at $M$ is $E = 6.0 \times 10^{-4} / 2.0 \times 10^{-8} = 3.0 \times 10^{4}\,\mathrm{N}/\mathrm{C}$, pointing east; $q' = -1.0 \times 10^{-8}\,\mathrm{C}$ placed at the same point feels $F = 1.0 \times 10^{-8} \times 3.0 \times 10^{4} = 3.0 \times 10^{-4}\,\mathrm{N}$ — pointing west.

Example 14.7 (A charged sphere)

A Van de Graaff sphere carries $Q = +5.0 \times 10^{-7}\,\mathrm{C}$ (a small charged sphere acts like a point charge at its center). At $d = 0.50\,\mathrm{m}$:

pointing radially away from the sphere. At $1.0\,\mathrm{m}$ it has dropped to a quarter of this: the $1/d^2$ of the force survives in the field.