A Zener diode, having breakdown voltage equal to $15V$, is used in a voltage regulator circuit shown in figure. The current through the diode is

In a p-n junction diode, the current I can be expressed as $I=I_{0}exp\left(\frac{eV}{2K_{B}T}-1\right)$, where $I_0$ is called the reverse saturation current, $V$ is the voltage across the diode and is positive for forward bias and negative for reverse bias, and $I$ is the current through the diode, $k_B$ is the Boltzmann constant $(8.6\times 10^{-5}eV/K)$ and $T$ is the absolute temperature. If for a given diode $I_o=5\times 10^{-12}$$A$ and $T=300K$, then
(a) What will be the forward current at a forward voltage of $0.6V$?(b) What will be the increase in the current if the voltage across the diode is increased to $0.7V$?(c) What is the dynamic resistance?(d) What will be the current if reverse bias voltage changes from $1V$ to $2V$?