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# Monthly Archives: May 2016

## Steady state error questions for GATE ECE

1) The transfer system of the system which will have more steady error for unit step input is
a) 80/(s+1)(s+2)(s+3)
b)120/s(s+1)(s+15)
c) 60/(s+0.5) (s+3)(s+5.5)
d)120/(s+1)(s+4)(s+15)

2)A unity feedback system has forward path transfer function G(s)=K/s(s+2). If the design specification is that the steady state error due to ramp input is 0.05,the value of K allowed is
a)20
b)40
c)10
d)80

3) When the gain  of the system is increased, the steady state error of the system
a)Increases
b) Decreases
c) Remains unchanged
d) May Increase or decrease

4) A unity feedback system has open loop transfer function G(s). The steady state error is zero for

a) Step input and type-1 G(s)                      b) Ramp input and type 1 G(s)

c) Step input and type -0 G(s)                     d) Ramp input and type 0 G(s)

5) A dc motor model G(s)= $\frac{1}{s(s+1)}$ is to obtain a steady state error of less than 0.1 for a unit ramp input. The above design specification can be achieved by a feed forward lead compensator whose steady state gain must be greater than

a) 100            b) 10       c) 1        d) 0.1

6) A unity feedback closed loop second order system has a transfer function  $\frac{81}{s^2+0.6s+9}$ and is excited by step input of 1 unit. The steady state error of the output is

a) 10       b) 0         c ) 1         d) 0.1

……………………..

1-d , 2-b, 3-b,4-a,5-b,6-d

## GATE : Calculate Gain and Phase margin from a transfer function questions

The open loop transfer function of negative feedback transfer function is G(s)H(s) = $\frac{1}{(1+s)^3}$

1) The phase crossover frequency in (rad/sec) is

a) $\sqrt{3}$  b) 3    c) 1/3    d) $\frac{1}{\sqrt{3}}$

2) The  value of gain margin in dB is

a) 24.08          b) 18.06         c) 12.04         d) 6.02

3) The gain crossover frequency is

a) 0         b) Infinity     c) $\sqrt{2}$     d) $\sqrt{2}$

4) The phase margin is

a) $\pi$       b) 0     c) $\pi/4$           d) $\pi/2$

5) The system with open loop transfer function G(s)H(s)= $\frac{1}{s(s^2+s+1)}$  has a gain margin of

a) -6 dB    b) 0 dB    c) 3.5 dB  d) 6 dB

Ans : b

6) The gain margin of a system having transfer function

G(s) H(s) = $\frac {2}{s(s+1)}$ is

a) 0        b) 3        c) 6       d) Infinity

## Quiz on GATE previous questions| BJT

1)For BJT, the common base current gain $\alpha$=0.98  and the collector base junction reverse bias saturation current $I_{CO}$= 0.6 uA. This BJT is connected in the common emitter mode and operated in the active region with base drive current $I_B$= 20 uA. The collector current $I_C$ for this mode of opertation is

a) 0.98 mA     b) 0.99 mA    c) 1 mA d) 1.01 mA

2)

In the circuit, what is the value of Current $I_o$

a) 0.5 mA   b) 2 mA    c)9.3 mA   d) 15 mA

3) What is the most noticeable effect of a small increase in temperature in the common emitter connected BJT?

a) Increase in $I_cbo$

b) Increase in output resistance

c) Decrease in forward current gain

d) Increase in forward current gain

4) In a common emitter amplifier, the unbypassed emitter resistance provides

a) Voltage shunt feedback

b) Current series feedback

c) negative voltage feedback

d) positive current feedback

5) If the differential voltage gain and common mode voltage gain of a differential amplifier are 48 dB and 2 dB respectively, then the common mode rejection ratio is

a) 23 dB

b) 25 dB

c) 46 dB

d) 50 dB

6) The gain of the amplifier(BJT) falls at higher frequencies due to

a) Internal capacitance of the device

b) Coupling capacitor at the input

c) Skin effect

d) Coupling capacitor at the output

7) Three identical amplifiers with each one having a voltage gain of 50 , input resistance of 1k ohm and output resistance of 250 ohm are cascaded. The circuit gain of the combined amplifier is

a) 49 dB

b) 51 dB

c) 98 dB

d) 102 dB

8) In a common emitter BJT amplifier , the maximum usable supply voltage is limited by

a) Avalanche breakdown of base emitter junction

b) Collector- Base breakdown voltage with emitter open

c) Collector – Emitter breakdown voltage with base open

d) Zener breakdown voltage of the emitter base junction