Chapter 17, Problem 94GP

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 35-fF capacitor (1 IF = 10-15F) is charged at 1.5 V, or“0” when uncharged at 0 V. (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.) Note: A DRAM cell is shown in Fig. 21-29.