21. Knowledge of the transfer function of a system is necessary for the calculation of :

(a) time constant

(b) output for a given input

(c) order of the system

(d) none of these

22. The steady – state error of a first – order system to a ramp input is equal to :

(a) the time constant of the system

(b) zero

(c) infinity

(d) none of these

23. For a second – order undamped system, the poles are :

(a) purely imaginary

(b) real and equal

(c) real and equal

(d) complex conjugate of each other

24. The transfer function is the ratio of :

(a) output to input

(b) the Laplace transform of output to the Laplace transform of input

(c) the Laplace transform of input to the Laplace transform of output

(d) the inverse Laplace transform of output to the inverse Laplace transform of input

25. Control systems are normally designed with damping factor :

(a) ξ = 0

(b) ξ = 1

(c) ξ > 1

(d) ξ < 1

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