What is the electric field strength when an electron increases its speed from 2.0x10^7 m/s to 4.0x10^7 m/s over a distance of 2.1 cm?
A) 1.9x10^6 N/C
B) 2.4x10^6 N/C
C) 3.2x10^6 N/C
D) 4.7x10^6 N/C