In the low - pass filter shown in the figure, for a cut - off frequency of 5 KHz, the value of R₂ (in k$$\Omega $$ ) is _________

In the ac equivalent circuit shown in the figure, if i$${_F}$$ is very large, the type of feedback is

In the voltage regulator circuit shown in the figure, the op - amp is ideal. The BJT has V_BE = 0.7 V and $$\beta $$ = 100, and the Zener voltage is 4.7 V. For a regulated output of 9 V, the value of R (in $$\Omega $$) is ______

In the circuit shown, the op-amp has finite input impedance, infinite voltage gain and zero input offset voltage. The output voltage V_out is