Chapter 24, Problem 10P

(II) In a dynamic random access memory (DRAM) computer chip, each memory cell chiefly consists of a capacitor for charge storage. Each of these cells represents a single binary-bit value of 1 when its 35-fF capacitor (1 fF = 10⁻¹⁵ F) is charged at 1.5 V, or 0 when uncharged at 0 V. (a) When it is 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 (through a variety of mechanisms) at a constant rate of 0.30 fC/s. How long does it take for the potential difference across this capacitor to decrease by 1.0% from its fully charged value? (Because of this leakage effect, the charge on a DRAM capacitor is “refreshed” many times per second.)