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

The voltage gain $${A_V}$$ of the circuit shown below is

The circuit shown is a

The feedback system shown below oscillates at $$2$$ rad/s when