Why is there a sudden increase in current in a Zener diode?

If the current in the Zener diode is five times the current in $R_1$ and the breakdown voltage of the diode is $6 \text{ V}$,find the value of $R$.

In the following circuit,the current flowing through the Zener diode is (in $\text{ mA}$)

$A$ Zener diode with a Zener voltage of $30 \text{ V}$ is connected in a circuit as shown in the figure. The maximum current through the Zener diode is: (in $\text{ mA}$)

For the given circuit (shown in part $(A)$), the time-dependent input voltage $v_{in}(t)$ and the corresponding output voltage $v_{o}(t)$ are shown in part $(B)$ and part $(C)$, respectively. Identify the components that are used in the circuit between points $X$ and $Y$.

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