Electronics Engineering - Online Test
Q1. 
If the electrical circuit of figure (b) is an equivalent of the coupled tank system of figure (a), then
Answer : Option D
Explaination / Solution:
No Explaination.
Q2. The two inputs of a CRO are fed with two stationary periodic signals. In the X-Y mode, the screen shows a figure which changes from ellipse to circle and back to ellipse with its major axis changing orientation slowly and repeatedly. The following inference can be made from this.
Answer : Option C
Explaination / Solution:
No Explaination.
Q3. 
Consider a baseband binary PAM receiver shown below. The additive channel noise n(t) is with power spectral density 
The lowpass filter is ideal with unity gain and cut-off frequency 1 MHz. Let Yk represent the random variable y(tk).
The lowpass filter is ideal with unity gain and cut-off frequency 1 MHz. Let Yk represent the random variable y(tk).Yk = Nk , if transmitted bit bk = 0
Yk = a + Nk if transmitted bit bk = 1
Where Nk represents the noise sample value. The noise sample has a probability density function, 
(This has mean zero and variance 2/α2). Assume transmitted bits to be equiprobable and threshold z is set to a/2
= 10-6 V.
(This has mean zero and variance 2/α2). Assume transmitted bits to be equiprobable and threshold z is set to a/2
= 10-6 V.The value of the parameter α
(in V-1) is
Answer : Option B
Explaination / Solution:
Let response of LPF filters
Noise variance (power) is given as
Q4. The polar plot of an open loop stable system is shown below. The closed loop system is
Answer : Option D
Explaination / Solution:
No Explaination.
Q5. In the following circuit employing pass transistor logic, all NMOS transistors
are identical with a threshold voltage of 1 V . Ignoring the body-effect, the
output voltages at P, Q and R are,
Answer : Option C
Explaination / Solution:
No Explaination.
Q6. An 8085 executes the following instructions
2710 LXI H, 30A0 H
2713 DAD H
2414 PCHL
All address and constants are in Hex. Let PC be the contents of the program counter and HL be the contents of the HL register pair just after executing PCHL. Which of the following statements is correct ?
Answer : Option C
Explaination / Solution:
2710H LXI H, 30A0H ; Load 16 bit data 30A0 in HL pair
2713H DAD H ; 6140H ⟶ HL
2714H PCHL ; Copy the contents 6140H of HL in PC
Thus after execution above instruction contests of PC and HL are same and that is 6140H
Q7. If the 12 Ω resistor draws a current of 1A as shown in the figure, the value of resistance R is
Answer : Option B
Explaination / Solution:
No Explaination.
Q8. A Linear Time Invariant system with an impulse response h(t) produces output y(t)
when input x(t) is applied. When the input x (t−τ) is applied to a system with impulse
response h(t − τ), the output will be
Answer : Option D
Explaination / Solution:
No Explaination.
Q9.
Consider a baseband binary PAM receiver shown below. The additive channel noise n(t) is with power spectral density The lowpass filter is ideal with unity gain and cut-off frequency 1 MHz. Let Yk represent the random variable y(tk).
The lowpass filter is ideal with unity gain and cut-off frequency 1 MHz. Let Yk represent the random variable y(tk).Yk = Nk , if transmitted bit bk = 0
Yk = a + Nk if transmitted bit bk = 1
Where Nk represents the noise sample value. The noise sample has a probability density function, (This has mean zero and variance 2/α2). Assume transmitted bits to be equiprobable and threshold z is set to a/2 = 10-6 V.
(This has mean zero and variance 2/α2). Assume transmitted bits to be equiprobable and threshold z is set to a/2 = 10-6 V.The probability of bit error is
Answer : Option D
Explaination / Solution:
Probability of error is given by
Q10. The first two rows of Routh's tabulation of a third order equation are as follows.
s3 2 4
s2 4 4.
This means there are
Answer : Option D
Explaination / Solution:
No Explaination.
