Quiz Electronics Engineering 4 August 2020

Quiz Electronics Engineering
Exam: NIC
Topic: Miscellaneous
Date: 04/08/2020

Each Question carries 1 Mark
Negative Marking: 1/4
Time: 10 Minutes

Q1. In a RS flip-flop no change occurs during
(a) set mode
(b) reset mode
(c) disabled mode
(d) prohibited mode

Q2. A Hilbert transformer is a
(a) non-linear system
(b) non-causal system
(c) time-varying system
(d) low-pass system

Q3. Which type of fading causes serious distortion of modulated signal:
(a) Selective fading
(b) Interference fading
(c) Absorption fading
(d) Polarization fading

Q4. For what value of unknown resistance X, the potential difference between B and D will be zero in the circuit shown:

(a) 5 Ω
(b) 7 Ω
(c) 6 Ω
(d) 4 Ω

Q5. What is peculiar about a TE_01 mode propagating in a circular wave guide?
(a) It has the largest attenuation
(b) It is the dominant mode
(c) It is used for long microwave communication
(d) It has least attenuation and attenuation decreases with increase in frequency

Q6. Interrupt Enable instruction is?
(a) DI
(b) EI
(c) EPI
(d) EAI

Q7. In a Schottky diode junction is formed between
(a) Two types of metals
(b) Two types of semiconductors
(c) Metal and semiconductor
(d) None of the above

Q8. The spectral density and autocorrelation function of white noise is
(a) Delta and uniform
(b) Gaussian and delta
(c) Gaussian and uniform
(d) Uniform and delta

Q9. When a number of resistances are connected in parallel, the total resistance will be
(a) Greater than the smallest resistance
(b) Less than the smallest
(c) Between smallest and greatest resistance
(d) zero

Q10. Dynamic memory cells are constructed using
(a) FETs
(b) MOSFETs
(c) Flip-flops
(d) transistors

SOLUTIONS

S1. Ans (c)
Sol. In RS Flip-Flop no change occurs when both the inputs are Low i.e. R = 0 & S = 0.

S2. Ans.(b)
Sol. A system is said to be causal if the output at any time depends only on the present and the past values. i.e. for t < 0, y(t) = 0.
The Hilbert transform is characterized by the Impulse response.
h(t) = 1/πt where, -∞ < t < ∞
and, h(t) ≠ 0 for t < 0.
We can see that it is defined for values t < 0. So, it is non-causal system.
The Hilbert transform is a non-causal linear time-invariant filter.

S3. Ans.(a)
Sol. In wireless communications, Fading is variation of the attenuation of a signal with respect to various parameters. Selective fading causes serious distortion of modulated signal

S4. Ans.(c)
Sol. It is a case of wheat stone bridge.

At balance condition,
⇒ 12 × 0.5 = 0.5 × (x+6)
⇒ 6 = 0.5 × (x+6)
⇒ 60/5 = x + 6
⇒ x + 6 = 12
So, x = 6 Ω

S5. Ans (d)

S6. Ans.(b)
Sol. Enable Interrupt (EI) – The interrupt enable FF is set and all interrupts are enabled following the execution of next instruction followed by EI. No flags are affected. After the system reset, the interrupt enable flip-flop is reset, thus disabling the interrupts. This instruction is necessary to enable all the interrupts except TRAP.

S7. Ans.(c)
Sol. The Schottky diode is a semiconductor diode. Its junction is formed of semiconductor and metal. It has a low forward voltage drop and a very fast switching action. It is also called as Schottky barrier diode or hot-carrier diode.

S8. Ans.(d)
Sol. The Power Spectral Density is the Fourier transform of the autocorrelation function. The PSD of white noise is a constant.
White noise describes a random process whose mean is zero. It has autocorrelation as a delta-function. The Power Spectral Density is the Fourier transform of the autocorrelation function. The PSD is uniform. Sx(f) = FT{ Rx(τ )}
Spectral density of white noise is

S9. Ans.(b)
sol. If resistances are connected in parallel then the equivalent resistance will be smaller than the smallest resistance.
For example –
If R_1 = 2 Ω and R_2 = 6 Ω is connected in parallel then,
Equivalent resistance (R_T ) is
1/R_T = 1/R_1 +1/R_2 = 1/3+1/6 = (2+1)/6
⇒ R_T = 6/3 Ω
So, R_T = 2 Ω
Hence, R_T<R_1. Thus proved.

S10. Ans (b)
Sol. DRAM memory technology has MOS technology at the heart of the design, fabrication and operation. Depending on the working of DRAM, it can be seen that the basic DRAM memory cell uses a capacitor to store each bit of data and a transfer device – a MOSFET – for acting as a switch.

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