This set of Control Systems Multiple Choice Questions & Answers (MCQs) focuses on “The Root Locus”.

1. Which one of the following applications software’s is used to obtain an accurate root locus for?

a) LISP

b) MATLAB

c) dBase

d) Oracle

2. Which one of the following is not the property of root loci?

a) The root locus is symmetrical about imaginary axis

b) They start from the open loop poles and terminate at the open loop zeroes

c) The breakaway points are determined from dK/ds = 0

d) Segments of the real axis are the part of the root locus if and only is the total number of real poles and zeroes to their right is odd.

3. Consider the loop transfer function K(s+6)/(s+3)(s+5) In the root locus diagram the centroid will be located at:

a) -4

b) -1

c) -2

d) -3

4. The breakaway point calculated mathematically must always lie on the root locus.

a) True

b) False

5. Which one of the following are correct?

The root locus is the path of the roots of the characteristic equation traced out in the s-plane?

a) As the input of the system is changed

b) As the output of the system is changed

c) As a system parameter is changed

d) As the sensitivity is changed

6. The addition of open loop zero pulls the root loci towards:

a) The left and therefore system becomes more stable

b) The right and therefore system becomes unstable

c) Imaginary axis and therefore system becomes marginally stable

d) The left and therefore system becomes unstable

7. What is the number of the root locus segments which do not terminate on zeroes?

a) The number of poles

b) The number of zeroes

c) The difference between the number of poles and zeroes

d) The sum of the number of poles and the number of the zeroes

8. If the gain of the system is reduced to a zero value, the roots of the system in the s-plane,

a) Coincide with zero

b) Move away from zero

c) Move away from poles

d) Coincide with the poles

9. If root loci plots of a particular control system do not intersect the imaginary axis at any point, then the gain margin of the system will be:

a) 0

b) 0.707

c) 1

d) Infinite

10. When the number of poles is equal to the number of zeroes, how many branches of root locus tends towards infinity?

a) 1

b) 2

c) 0

d) Equal to number of zeroes