A lightning discharge may take place between a charged cloud and the Earth’s surface once the electric field strength in the air between them reaches $25\,\text{kN C}^{-1}$. The diagram illustrates the electric field between the cloud base and the Earth’s surface. What is the least potential difference between the Earth and the base of a cloud, $2\,\text{km}$ high, needed for lightning to occur?
- A12.5 MV
- B25 MV
- C50 MV
- D100 MV