A pair of horizontal parallel plate conductors is separated by an air gap of $5.0\,\text{mm}$. The lower plate is earthed, while the upper plate is held at $+50\,\text{V}$. What is the electric field strength $E$ at a point halfway between the plates?
- A$1.0 \times 10^4\,\text{V m}^{-1}$ downwards
- B$1.0 \times 10^4\,\text{V m}^{-1}$ upwards
- C$2.0 \times 10^4\,\text{V m}^{-1}$ downwards
- D$2.0 \times 10^4\,\text{V m}^{-1}$ upwards