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 โ1โ when its 35-fF capacitor \(\left( {{\bf{1}}\;{\bf{fF = 1}}{{\bf{0}}^{{\bf{ - 15}}}}\;{\bf{F}}} \right)\) is charged at 1.5 V, or โ0โ when uncharged at 0 V.
(a) When fully charged, how many excess electrons are on a cell capacitorโs negative plate?
(b) After charge has been placed on a cell capacitorโs plate, it slowly โleaksโ off at a rate of about \({\bf{0}}{\bf{.30}}\;{\bf{fC/s}}\). 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 โrefreshedโ many times per second.) Note: A DRAM cell is shown in Fig. 21โ29.