# Formula: Charge in Radial E-field Energy    Electric charge    Distance

## Potential energy

Unit
Potential energy of a charged particle with charge $$\class{red}{q}$$ in an external electric field. The charge $$\class{red}{q}$$ is at a distance $$r$$ from the source charge $$\class{red}{Q}$$ which generates the electric field.

## Electric charge

Unit
Electric charge of the particle for which the potential energy is calculated. To bring a positive charge from infinity to the point $$P$$ to the positive charge $$\class{red}{Q}$$, energy must be invested.

## Source charge

Unit
Electric charge that generates the electric field.

## Distance

Unit
Distance of the small charge $$\class{red}{q}$$ from the source charge $$\class{red}{Q}$$.

## Vacuum Permittivity

Unit
The vacuum permittivity is a physical constant that appears in equations involving electromagnetic fields. It has the following experimentally determined value: $$\varepsilon_0 ~\approx~ 8.854 \, 187 \, 8128 ~\cdot~ 10^{-12} \, \frac{\mathrm{As}}{\mathrm{Vm}}$$

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