Consider the mutual repulsion of two positively charged bodies A and B(at point P). How does each one know the other is there?

As a result of the charge that body A carries, the properties of the space around it are modified. Body A produces an electric field at point P (where B is at).

$$\vec{E} = \lim_{q_{0} \to 0} \frac{1}{q_{0}} \vec{F_{0}}$$

**Important note:** You might think that as q_{0} goes to 0, the whole expression will go to infinity. It is correct in the mathematical point of view. But, as physicists are rather sloppy in mathematical notations, the above expression actually means that the point charge (q_{0}) must be small.

As a result of the charge that “particle” B carries B senses how space has been modified at P.

$$ \vec {F_{0}} = q_{0} \vec{E}$$

**Analogy:** You can think of the electric field as a spider web. The spider (Body A) sets up a web (electric field). A fly (Body B) encounters the spider web (electric field) and felt a force.

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