6.18 Consider an npn transistor operated in the active mode and represented by the model of Fig. 6.5(d). Let the transistor be connected as indicated by the equivalent circuit shown in Fig. 6.6(b). It is required to calculate the values of R B and R C that will establish a collector current I C of 0.5 mA and a collector-to-emitter voltage V CE of 1 V. The BJT is specified to have β=50 and I S = 5×10 −15 A.