[填空题]
A lightning flash trn esy rkw7dwa922ol *ezm-8b6ansfers 6+au 0wt ueim(cxy(z..kx9te4.0 C of charge and 4.2 MJ of energy to the Earth.
(a) Across what potential difference did it travel? $ \times10^{ 6}\,V$
(b) How much water could this boil and vaporize, starting from room temperature? kg