Calculating the Force Exerted on a Point Charge by an Electric Field

Since we know the electric field strength and the charge in the field, the force on that charge can be calculated using the definition of electric field $\mathbf{\text{E}}=\mathbf{\text{F}}/q$ rearranged to $\mathbf{\text{F}}=q\mathbf{\text{E}}$.

The magnitude of the force on a charge $q=-0\text{.}\text{250}\text{μC}$ exerted by a field of strength $E=7\text{.}\text{20}\times {\text{10}}^5$ N/C is thus,

Because $q$ is negative, the force is directed opposite to the direction of the field.

The force is attractive, as expected for unlike charges. (The field was created by a positive charge and here acts on a negative charge.) The charges in this example are typical of common static electricity, and the modest attractive force obtained is similar to forces experienced in static cling and similar situations.