During a lightning discharge between a cloud and the ground, the mean current is $1.5 \times 10^4\,\text{A}$. The lightning transfers $3.0 \times 10^8\,\text{J}$ of energy and has a duration of $2.0 \times 10^{-4}\,\text{s}$. What is the mean electromotive force (e.m.f.) between the cloud and the ground?
- A$4.0\,\text{V}$
- B$100\,\text{V}$
- C$1.0 \times 10^8\,\text{V}$
- D$9.0 \times 10^8\,\text{V}$