1. If the electric field exceeds about 3*10^6 N/C in air, a spark occurs. Approximately, what is the absolute value of the maximum possible potential difference between the plates of a capacitor whose gap is 3 mm, without causing a spark in the air between them?
2. A capacitor with a gap of 2 mm has a potential difference from one plate to the other of 30 volts. What is the magnitude of the electric field between the plates?