Answer
a. $3.22 \Omega$
b. $61.1 \Omega$.
Work Step by Step
a. First evaluate $\frac{eV}{kT}$ for the given voltage and temperature.
$\frac{(1.6\times10^{-19}C)(0.085V)}{(1.381\times10^{-23}J/K)(293K)}=3.361$
Now find the resistance at this voltage using equation 42.22 and the given saturation current.
$R=V/I=V/((0.950mA)(e^{eV/kT}-1))=3.22 \Omega$
b. Repeat the calculation using this voltage, to find a resistance of $61.1 \Omega$.
Reversing the voltage made a huge change in the resistance of the diode.
