{{fa>pencil?32}} {{drawio>electrical_engineering_2:coulombkraftgeometrieiii.svg}} Given is an arrangement of electric charges located in a vacuum (see picture on the right). \\ The charges have the following values: \\ $Q_1= 2 ~\rm{µC}$ (point charge) \\ $Q_2=-4 ~\rm{µC}$ (point charge) \\ $Q_3= 0 ~\rm{C}$ (infinitely extended surface charge) $\varepsilon_0=8.854\cdot 10^{-12} ~\rm{F/m}$ , $\varepsilon_r=1$ 1. calculate the magnitude of the force of $Q_2$ on $Q_1$, without the force effect of $Q_3$. {{icon>eye}} Result \begin{align*} |\vec{F}_C| = 0.3595 ~\rm{N} \rightarrow 0.36 ~\rm{N} \end{align*} \\ 2. is this force attractive or repulsive? {{icon>eye}} Solution The force is attractive because the charges have different signs. \\ \\ \\ Now let $Q_2=0$ and the surface charge $Q_3$ be designed in such a way that a homogeneous electric field with $E_3=100 ~\rm{kV/m}$ results. \\ What force (magnitude) now results on $Q_1$? {{icon>eye}} Result \begin{align*} |\vec{F}_C| = 0.4 ~\rm{N} \end{align*} \\