In the dynamic random access memory (DRAM) of a computer, each memory cell contains a capacitor for charge storage. Each of these cells represents a single binary-bit value of "1" when its 40-fF capacitor (1 fF=10¹⁵) is charged at 1.5V, or "0" when uncharged at 0V.

a. When fully charged, how many excess electrons are on a cell capacitor's negative plate?

b. After charge has been placed on a cell capacitor's plate, it slowly "leaks" off at a rate of about 0.30 fC/s. How long does it take for the potential difference across this capacitor to decrease by 2.0%% from its fully charged value? (Because of this leakage effect, the charge on a DRAM capacitor is "refreshed" many times per second.)