EC GATE 2009 (Test 2)



Tag: ec gate 2009
Q.1
The ratio of the mobility to the diffusion coefficient in a semiconductor has the units
A.

V-1

B.

Cm. V1

C.

V. Cm-1

Answer : Option A
Explaination / Solution:



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Q.2
In the circuit below, the diode is ideal. The voltage V is given by 

A. min (Vi,1)
B. max (Vi,1)
C. min (-Vi,1)
D. max (-Vi,1)
Answer : Option A
Explaination / Solution:

Let diode be OFF. In this case 1 A current will flow in resistor and voltage across resistor will be V = 1.V
Diode is off, it must be in reverse biased, therefore
Vi- 1 > 0 " Vi > 1
Thus for Vi > 1 diode is off and V = 1V
Option (B) and (C) doesn’t satisfy this condition.
Let Vi < 1. In this case diode will be on and voltage across diode will be zero and 
V = Vi
Thus V = min(Vi,1)


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Q.3
Consider the following two statements about the internal conditions in a n - channel MOSFET operating in the active region.
S1 : The inversion charge decreases from source to drain
S2 : The channel potential increases from source to drain.
Which of the following is correct?
A. Only S2 is true
B. Both S1 and S2 are false
C. Both S1 and S2 are true, but S2 is not a reason for S1
D. Both S1 and S2 are true, and S2 is a reason for S1
Answer : Option D
Explaination / Solution:

Both S1 and S2 are true and S2 is a reason for S1.

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Q.4
The peak electric field in the device is 
A. 0.15 MV . cm-1, directed from p -region to n -region
B. 0.15 MV . cm-1, directed from n -region to p -region
C. 1.80 MV . cm-1, directed from p-retion to n -region
D. 1.80 MV . cm-1, directed from n -region to p -region
Answer : Option B
Explaination / Solution:

The peak electric field in device is directed from p to n and is 



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Q.5
For small increase in VG beyond 1V, which of the following gives the correct description of the region of operation of each MOSFET
A. Both the MOSFETs are in saturation region
B. Both the MOSFETs are in triode region
C. n-MOSFETs is in triode and p -MOSFET is in saturation region
D. n- MOSFET is in saturation and p -MOSFET is in triode region
Answer : Option D
Explaination / Solution:

For small increase in VG beyond 1 V the n - channel MOSFET goes into saturation as VGS + ive and p - MOSFET is always in active region or triode region.

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Q.6
A white noise process X(t) with two-sided power spectral density 1 X 10-10  W/HZ is input to a filter whose magnitude squared response is shown below.


A.

5 X 10-10  W

B.

1 X 10-6  W

C.

2 X 10-6  W

D.

1 X 10-5  W

Answer : Option C
Explaination / Solution:
No Explaination.


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Q.7
Which of the following statements is true regarding the fundamental mode of the metallic waveguides shown ?

A. Only P has no cutoff-frequency
B. Only Q has no cutoff-frequency
C. Only R has no cutoff-frequency
D. All three have cutoff-frequencies
Answer : Option A
Explaination / Solution:

Rectangular and cylindrical waveguide doesn’t support TEM modes and have cut off frequency. Coaxial cable support TEM wave and doesn’t have cut off frequency.


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Q.8

For a message signal and carrier of frequency fc which of thefollowing represents a single side-band (SSB) signal ?

A.
B.
C.
D.
Answer : Option C
Explaination / Solution:



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Q.9
The time domain behavior of an RL circuit is represented by  For an initial current of
For an initial current of the steady state value of the current is given by 
A.
B.
C.
D.
Answer : Option A
Explaination / Solution:

Steady state all transient effect die out and inductor act as short circuits and forced response acts only. It doesn’t depend on initial current state. From the given time domain behavior we get that circuit has only R and L in series with vThus at steady state 

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Q.10
Consider a system whose input x and output y are related by the equation where h(t) is shown in the graph.

Which of the following four properties are possessed by the system ?
BIBO : Bounded input gives a bounded output.
Causal : The system is causal,
LP : The system is low pass.
LTI : The system is linear and time-invariant.
A. Causal, LP
B. BIBO, LTI
C. BIBO, Causal, LTI
D. LP, LTI
Answer : Option B
Explaination / Solution:

Here h(t) ! 0 for t < 0. Thus system is non causal. Again any bounded input x(t) gives bounded output y(t). Thus it is BIBO stable.

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