The output impedance of a non-ideal operational amplifier is denoted by Z_out. The variation in the magnitude of Z_out with increasing frequency, f, in the circuit shown below, is best represented by

The current gain (I_out/I_in) in the circuit with an ideal current amplifier given below is

The Bode magnitude plot of a first order stable system is constant with frequency. The asymptotic value of the high frequency phase, for the system, is $$-$$180$$^\circ$$. This system has

The open loop transfer function of a unity gain negative feedback system is given by $$G(s) = {k \over {{s^2} + 4s - 5}}$$. The range of k for which the system is stable, is