Quick questions on Electric fields: Coulomb's law, field strength and potential - Edexcel A-Level Physics

Around a point charge the field is radial: $E = \frac{1}{4\pi\varepsilon_0}\frac{Q}{r^2}$, pointing away from a positive charge. Between two parallel charged plates the field is uniform: $E = \frac{V}{d}$, where $V$ is the potential difference and $d$ the plate separation, with field lines running straight from the positive to the negative plate.

Potential is a scalar, so potentials from several charges simply add. Unlike field strength (inverse square), potential falls off as $\frac{1}{r}$. The work done moving a charge between two points depends only on the potential difference, not the path taken, because the electrostatic field is conservative.

A particle of charge $Q$ in a uniform field feels a constant force $F = EQ$ and hence a constant acceleration $a = \frac{EQ}{m}$ in the direction of the field (for a positive charge) or against it (for a negative charge). If it enters at right angles to the field with speed $u$, it keeps a constant velocity along the entry direction and accelerates uniformly across the field, tracing a parabola exactly as a projectile does under gravity.

Define electric field strength. [1 mark]

Two parallel plates $5.0$ mm apart have a potential difference of $100$ V. Find the field strength between them. [2 marks]

State how electric field strength and electric potential each depend on distance from a point charge. [2 marks]