Quiz Electronics and Communication Engineering
Each Question carries 2 Mark
Negative Marking: 1/3
Time: 30 Minutes
Q1. A Master-Slave flip-flop has the characteristic that
(a) change in the output occurs when the state of the slave is affected
(b) change in the output occurs when the state of the master is affected
(c) change in the input immediately reflected in the output
(d) both the master and the slave states are affected at the same time
Q2. A box contains 10 Screws, 3 of which are defective. Two screws are drawn at random with replacement. The probability that none of the two screws is defective will be
(d) None of these
Q3. If the number of bits per sample in a PCM system is increased from and n to (n+1), the improvement in signal to quantization nose ratio will be
(a) 3 dB
(b) n dB
(c) 2 n dB
(d) 6 dB
Q4. Germanium is not used in the fabrication of thyristors because
(a) It is much costlier than silicon
(b) It has much lower thermal conductivity than silicon
(c) Its breakdown voltage is much larger than that of silicon
(d) Both (a) and (b)
Q5. A device that works in conjunction with a computer but not as part of it is called
(c) Peripheral device
Q6. An excitation is applied to a system at t = T and its response is zero for -∞ < t < T. Such a system is a
(a) unstable system
(b) non-causal system
(c) stable system
(d) causal system
Q7. A 10Ω resistor, a 1H inductor and 1µF capacitor are connected in parallel. The combination is driven by a unit step current. Under the steady state condition, the source current flows through:
(a) the inductor
(b) the resistor
(c) the capacitor only
(d) all the three elements
Q8. The dominant mode in a rectangular waveguide is TE10, because this mode has
(a) no attenuation
(b) no cut-off
(c) the highest cut-off wavelength
(d) no magnetic field component
Q9. In delta modulation, the slope overload distortion can be reduced by
(a) decreasing the step size
(b) increasing the step size
(c) decreasing the sampling noise
(d) decreasing the granular noise
Q10. Signal Flow Graph is used to find
(a) Transfer function of the system
(b) Controllability of the system
(c) Stability of the system
(d) Poles of the system
Sol. In MS FF, Master is applied with input clock and Slave is applied with inverted clock. Due to this Master & Slave output does not changes simultaneously. In MS FF output changes when Slave output changes.
Sol. Population is finite and sampling is done with replacement so probability does not change from trial to trial. The probability of obtaining x successes from n trials is given by the binomial distribution formula,
P(X=x) = nCx px(1-p)n-x
where p is the probability of success and (1-p) is probability of failure.
Probability of non-defective piece (1-p) = (10-3)/10 = 7/10
Probability of defective piece (p) = 3/10
Probability of none of the two screws are defective
x=0 (no defective)
So, P(X=0) = 2C₀ (3/10)^0 (7/10)^2
= 0.49 = 49%
Sol. We know that,
(SQNR)dB = (S/N_Q )_dB= 1.76 + 6n
For n bits we get,
(SQNR)dB1 = 1.76 + 6n ……………..(1)
If n changes to n+1 bits, then
(SQNR)dB2 = 1.76 + 6(n + 1) ……………..(2)
Solving (1) and (2), we get
(SQNR)dB1 – (SQNR)dB2 = 1.76 + 6n + 6 – 1.76 – 6n = 6dB
So, For changing of bits from n to n+1, the improvement in Signal to Quantization nose ratio will be 6dB.
Sol. Germanium is not considered over Silicon due to following reasons-
1. It has high reverse leakage current.
2. In high power applications, Si based devices can tolerate high power as compared to Ge.
3. Ge has lower thermal conductivity so its thermal resistance is more.
4. It is costlier than Si because Si is found in large amount in nature.
Due to these reasons Germanium thyristors suffer from more losses, high temperature rise and so its operating life decreases.
Sol. Peripheral device are the external device which are connected to the computer for performing some specific task e.g. printer. A printer is not part of computer, it only does the jobs instructed by the computer.
Sol. A system is Causal, if the response of system is zero before the application of the excitation. Here, The system is excited at t = T so, it is a Causal System.
Sol. At steady state, Inductor behaves as short circuit and capacitor behaves as open circuit. So, under steady state condition the source current flows through the inductor.
Sol. TE10 is considered dominant mode because it has lowest cut off frequency which is equal to c/2a. We know that frequency is the inverse of wavelength i.e. (λ) = 1/f . As cut off frequency is minimum so it will have maximum wavelength.
Sol. In case of Slope Overload Distortion, the slope of analog signal is much higher than that of approximated digital signal.
Condition to avoid slop overload in delta modulation is
Δ/T_S ≥ (dm(t))/dt
So, from above equation we can say that slope overload distortion can be avoided if step size is increased.
Sol. The Signal Flow Graph (SFG) does tell about the Stability, Controllability and Poles of the System. With the help of SFG we construct the Transfer function of the system.