Lightning may form 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 from the base of a cloud to the Earth’s surface. Calculate the smallest potential difference between the Earth and the base of a cloud, $2.0\,\text{km}$ high, needed for lightning to happen?
- A$12.5\,\text{MV}$
- B$25\,\text{MV}$
- C$50\,\text{MV}$
- D$100\,\text{MV}$