If the unit step response of a network is $$(1-e^{-\alpha t})$$, then its unit impulse response is

In the following circuit, the switch S is closed at t=0. The rate of change of current $$\frac{di}{dt}(0^+)$$ is given by

The condition on R, L and C such that the step response y(t) in figure has no oscillations, is

For the R-L circuit shown in Fig, the input voltage. v_i(t) = u (t) The current i(t) is