P19-070 – Electric Force

Definition: electric force

A charge $q$ placed in an electric field $\overrightarrow{E}$ experiences an electric force ${\overrightarrow{F}}_E$ given by

\boxed{{\overrightarrow{F}}_E=q\overrightarrow{E}}

The electric force acting on a positive charge $q_1$ points in the same direction as the electric field $\overrightarrow{E}$.

The electric force acting on a negative charge $-q_2$ points in the direction opposite $\overrightarrow{E}$.

Note: if instead of a positive point charge $q$ you consider a negative point charge $-q$, then the formula becomes

\boxed{{\overrightarrow{F}}_E=-q\overrightarrow{E}}

where the negative sign can be interpreted as the direction of ${\overrightarrow{F}}_E$ being opposite that of $\overrightarrow{E}$. Thus, the same formula conveniently applies for both positive and negative point charges.

Note: a point charge $q$ CANNOT feel the electric field that it creates. It can only experience the electric force if it is placed in an electric field created by some other charge distribution!