-
The Bode magnitude plot of the transfer function
G(s) = K(1 + 0.5s)(1 + as) I shown below : s 
1 + s 
(1 + bs) 1 + s 8 36 Note that – 6 dB/octave = – 20dB/decade. The value of a is ______________. bK 
-
- 0.75
- 25
- 7.5
- None of the above
Correct Option: A
From the magnitude plot,
| G(s) = | K |  | 1 + |  | | 1 + | | ||||||
| 2 | 4 | ||||||||||||
| S | | 1 + | | | 1 + | | | 1 + | | ||||
| 8 | 24 | 36 | |||||||||||
Now comparing with given transfer function
| a = | ; b = | |||
| 4 | 24 |
For finding K:
K = (ω)n : where n is no. of poles from the given plot
∴ K = (8)1
| Now , | = | × 8 = 0.75 | ||
| bk | 24 |
