EC GATE 2011 - Online Test
Q1. In the circuit shown below, capacitors C1 and C2 are very large and are shorts
at the input frequency. vi is a small signal input. The gain magnitude 
at 10
M rad/s is
at 10
M rad/s is
Answer : Option A
Explaination / Solution:
For the parallel RLC circuit resonance frequency is,
which is maximum
Thus given frequency is resonance frequency and parallel RLC circuit has
maximum impedance at resonance frequency
Gain of the amplifier is 
where ZC is impedance of parallel RLC
circuit.
where ZC is impedance of parallel RLC
circuit.Hence at this frequency (ωr), gain is
which is maximumTherefore gain is maximum at ωr = 10 /sec M rad .
Q2. Drift current in the semiconductors depends upon
Answer : Option C
Explaination / Solution:
No Explaination.
Q3. A Zener diode, when used in voltage stabilization circuits, is biased in
Answer : Option B
Explaination / Solution:
Zener diode operates in reverse breakdown region.
Q4. There are two candidates P and Q in an election. During the campaign, 40% of the voters promised to vote for P, and rest for Q. However, on the day of election 15% of the voters went back on their promise to vote for P and instead voted forQ. 25% of the voters went back on their promise to vote for Q and instead voted for P. Suppose, P lost by 2 votes, then what was the total number of voters?
Answer : Option A
Explaination / Solution:
No Explaination.
Q5. A silicon PN junction is forward biased with a constant current at room temperature. When the temperature is increased by 10ºC, the forward bias voltage across the PN junction
Answer : Option D
Explaination / Solution:
For every 1º C increase in temperature, forward bias voltage across diode decreases by 2.5 mV. Thus for 10º C increase, there us 25 mV decreases
Q6. The fuel consumed by a motorcycle during a journey while traveling at various
speeds is indicated in the graph below.
The distances covered during four laps of the journey are listed in the table below
From the given data, we can conclude that the fuel consumed per kilometre was
least during the lap
Answer : Option B
Explaination / Solution:
Since fuel consumption/litre is asked and not total fuel consumed, only average speed is relevant. Maximum efficiency comes at 45 km/hr, So least fuel consumer per litre in lap Q
Q7. In the circuit shown below, for the MOS transistors, 
and
the threshold voltage VT = 1 V. The voltage Vx at the source of the upper
transistor is
and
the threshold voltage VT = 1 V. The voltage Vx at the source of the upper
transistor is
Answer : Option C
Explaination / Solution:
Given circuit is shown below.
Thus our assumption is true and Vx = 3 V.
For transistor M2,
Since 
thus M2 is in saturation.
By assuming M1 to be in saturation we have
thus M2 is in saturation.
By assuming M1 to be in saturation we haveTaking positive root,
Thus our assumption is true and Vx = 3 V.
Q8. For a BJT the common base current gain α = 0.98 and the collector base
junction reverse bias saturation current ICO = 0.6 μA. This BJT is connected in
the common emitter mode and operated in the active region with a base drive
current IB = 204 A. The collector current IC for this mode of operation is
Answer : Option D
Explaination / Solution:
In active region, for common emitter amplifier,
Substituting ICO = 0.6 μA and IB = 204 μA in above eq we have,
IC = 1.01 mA
Q9. For the BJT QL in the circuit shown below, 
The
switch is initially closed. At time t = 0, the switch is opened. The time t at
which Q1 leaves the active region is
The
switch is initially closed. At time t = 0, the switch is opened. The time t at
which Q1 leaves the active region is
Answer : Option C
Explaination / Solution:
Applying KCL at collector
with time, the capacitor charges and voltage across collector changes from 0
towards negative.
Q10. The channel resistance of an N-channel JFET shown in the figure below is 600Ω when the full channel thickness (tch) of 10μm is available for conduction. The
built-in voltage of the gate P+ N junction (Vbi) is -1 V. When the gate to source
voltage (VGS) is 0 V, the channel is depleted by 1 μm on each side due to the built
in voltage and hence the thickness available for conduction is only 8 μm
The channel resistance when VGS = -3 V is
Answer : Option B
Explaination / Solution:
