A lightning discharge can take place between a charged cloud and the Earth’s surface when the electric field strength in the air between them reaches $25\,\text{kN C}^{-1}$. The diagram illustrates the electric field between the bottom of a cloud and the Earth’s surface. What is the least potential difference between the Earth and the bottom of a cloud, $2\,\text{km}$ above the ground, for lightning to occur?
- A$12.5\,\text{MV}$
- B$25\,\text{MV}$
- C$50\,\text{MV}$
- D$100\,\text{MV}$