When you walk across a carpeted floor while wearing socks on a dry day, your socks (and hence you) become charged by rubbing with the carpet. When your finger approaches a metal doorknob, you notice that a spark jumps across the air gap between your finger and the doorknob when that gap is less than about 1 mm. What is the approximate magnitude of the electric field between your finger and the doorknob just before the spark jumps? What is the potential difference between your finger and the doorknob?