Electronics Engineering - Online Test
Q1. The transfer function of a discrete time LTI system is given by
Consider the following statements:
S1: The system is stable and causal for ROC: |z| > 1/2
S2: The system is stable but not causal for ROC: |z| < 1/4
S3: The system is neither stable nor causal for ROC: 1/4 < |z| < 1/2
Which one of the following statements is valid ?
Answer : Option C
Explaination / Solution:
By partial fraction H(z) can be written as
For ROC : |z| > 1/2
Thus system is causal. Since ROC of H(z) includes unit circle, so it is stable also. Hence S1 is True
For ROC : |z| < 1/4
System is not causal. ROC of H(z) does not include unity circle, so it is not stable and S3 is True
Q2. Consider a silicon sample at T=300K, with a uniform donor density 
illuminated uniformly such that the optical generation rate
is 
throughout the sample. The incident radiation is turned off at 𝑡=0.
Assume low-level injection to be valid and ignore surface effects. The carrier lifetimes are 
illuminated uniformly such that the optical generation rate
is throughout the sample. The incident radiation is turned off at 𝑡=0.
Assume low-level injection to be valid and ignore surface effects. The carrier lifetimes are The hole concentration at t = 0 and the hole concentration at t = 0.3μs, respectively, are
Answer : Option A
Explaination / Solution:
Q3. The Boolean expression 
converted into the canonical product of sum (POS) form is
converted into the canonical product of sum (POS) form is
Answer : Option A
Explaination / Solution:
We have the SOP Boolean form,
Hence, in POS form, we have
Q4. A transmission line of characteristic impedance 50 W is terminated in a load
impedance ZL. The VSWR of the line is measured as 5 and the first of the
voltage maxima in the line is observed at a distance of λ/4 from the load. The
value of ZL is
Answer : Option A
Explaination / Solution:
Since voltage maxima is observed at a distance of λ/4 from the load and we know
that the separation between one maxima and minima equals to λ/4 so voltage
minima will be observed at the load, Therefore load can not be complex it must
be pure resistive.
also RL = R0/s (since voltage maxima is formed at the load)
RL = (50/5)Ω
Q5. The current I in the circuit shown is
Answer : Option A
Explaination / Solution:
Q6. A continuous time LTI system is described by
Assuming zero initial conditions, the response y(t) of the above system for the input 
is given by
is given by
Answer : Option B
Explaination / Solution:
System is described as
Taking laplace transform on both side of given equation
Transfer function of the system
By Partial fraction
Taking inverse laplace transform
Q7.
A unity negative feedback closed loop system has a plant with the transfer function 
and a controller GC (s) in the
and a controller GC (s) in thefeed forward path. For a unit set input, the transfer function of the controller that gives minimum steady state error is
Answer : Option D
Explaination / Solution:
Steady state error is given as
ess will be minimum if 
is maximum In option (D)
is maximum In option (D)
Q8. In the circuit shown below, the knee current of the ideal Zener dioide is 10 mA
. To maintain 5 V across RL, the minimum value of RL in Ω and the minimum
power rating of the Zener diode in mW, respectively, are
Answer : Option B
Explaination / Solution:
No Explaination.
Q9. If X = 1 in logic equation 
Then
Then
Answer : Option D
Explaination / Solution:
Substituting X = 1 and
we get
1 + A = 1 and 0 + A = A
Substituting X = 1 and
we get 1 + A = 1 and 0 + A = A
Q10. x(t) is a stationary random process with auto-correlation function. 
This process is passed through the system shown below. The
power spectral density of the output process y(t) is
This process is passed through the system shown below. The
power spectral density of the output process y(t) is
Answer : Option A
Explaination / Solution:
The given circuit can be simplified as
Power spectral density of output is
