The sinusoidal ac source in the figure has an rms value of $${{20} \over {\sqrt 2 }}\,V.$$ Considering all possible values of $${R_L},\,\,$$ the minimum value of $${R_s}$$ in $$\Omega $$ to avoid burnout of the Zener diode is ______.

The $$i$$-v characteristics of the diode in the circuit given below are $$$i = \left\{ {\matrix{ {{{v - 0.7} \over {500}}A,} & {v \ge 0.7\,V} \cr {0A,} & {v < 0.7\,V} \cr } } \right.$$$

The current in the circuit is

Assuming that the diodes an ideal in the given circuit, the voltage $${V_0}$$ is

The following circuit has a voltage source $${V_s}$$ as shown in the graph. The current through the circuit is also shown

The element connected between $$' a '$$ and $$' b '$$ could be