21) If the gain of the open loop system is doubled, the gain margin of the system is
a) not affected
d) one fourth of original value
22) Which one of the following is a disadvantage of proportional controller ?
a) it destabilises the system
b) it producer offset
c) it makes response faster
d) it has very simple implementation
23) How many roots with positive real parts do the equation s3 + s2 – s + 1 = 0 have ?