Physics - Semiconductors Question with Solution | TestHub

At time $t=0,$ voltage across the first zener diode is increases linearly till it reaches it's breakdown voltage of $4 \mathrm{V}$, after that voltage increases linearly till it reaches the breakdown voltage of second zener diode,

As soon as voltage across the zener diode reaches the breakdown voltage of $6 \mathrm{V}$ of second zener diode, volatge becomes constant and doesn't change with time.