What is Coulomb’s law?

Coulomb’s law gives the electric force between two point charges: F = k·q₁·q₂ / r², where k = 8.99 × 10⁹ N·m²/C². Like charges repel, unlike charges attract, and the force falls off with the square of the distance.

What do electric field lines show?

They show the direction of the electric force on a positive test charge. They start on positive charges and end on negative ones, and lines drawn closer together mean a stronger field.

How do you calculate the electric field of a point charge?

E = k·q / r², in newtons per coulomb (N/C). The force on a charge q in that field is F = q·E.

Two equal and opposite charges close together. Its field lines leave the positive charge and curve round to the negative one.

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Electric Fields

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Electric fields

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E at test charge—

Force on test charge—