A pair of horizontal parallel plate conductors is spaced by 5.0\ \text{mm} in air. The lower plate is earthed, while the upper plate is at +50\ \text{V}. What is the electric field strength E at the midpoint 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