4.38 a diode operates in a series circuit with a resistance r and a dc source v. a designer, considering using a constant-voltage model, is uncertain whether to use 0.7 v or 0.6 v for vd. for what value of v is the difference in the calculated values of current only 1%? for v = 3 v and r = 1 k! , what two current estimates would result from the use of the two values of vd? what is their percentage difference?