Quiz Electronics Engineering 6 Aug 2020

Quiz Electronics Engineering
Exam: NIC
Topic: Miscellaneous
Date: 06/08/2020

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

Q1. The E.M. waves are reflected by the ionosphere due to their interaction with
(a) electrons
(b) protons
(c) ultraviolet rays
(d) none of the above

Q2. The time-constant of the network shown in the figure is

(a) 2CR
(b) CR
(c) CR/4
(d) CR/2

Q3. In Schottky barrier diode current flows because of
(a) majority and minority carriers
(b) minority carriers
(c) majority carriers
(d) none of these

Q4. Frequency Shift Keying is basically a method involving
(a) phase modulation
(b) amplitude modulation
(c) frequency modulation
(d) none of the above

Q5. In binary number system the first digit (bit) from left to right is called as
(a) LSB, Least Significant Bit
(b) MSB, Most Significant Bit
(c) First Bit
(d) Last Bit

Q6. A transistor – terminal current is positive when the
(a) current is due to flow of electrons
(b) current is due to flow of holes
(c) electrons flow into the transistor at the terminal
(d) electrons flow out of the transistor at the terminal

Q7. The binary division 11000_2÷100_2 gives…..
(a) 11
(b) 101
(c) 110
(d) 1100

Q8. The pre-emphasis circuit is used
(a) after demodulation
(b) before demodulation
(c) to increase or emphasize the amplitude of low frequency components of signal
(d) None of these

Q9. A medium is said to be isotropic when
(a) ε = μ
(b) ε = μ σ
(c) ε is zero
(d) ε is a scalar constant

Q10. A DC voltage V is applied to a series RL circuit. The steady state current is
(a) V/R
(b) V/L
(c) V/√(R^2+L²)
(d) zero

SOLUTIONS

S1. Ans (a)
Sol. The ionosphere is a upper region of the atmosphere. It consists of large concentrations of free ions and electrons. Due to large concentrations of free ions it is called ionosphere. It is the free electrons that affect the radio waves and radio communications. In particular the ionosphere is widely known for affecting signals on the short-wave radio bands where it “reflects” signals enabling these radio communications signals to be heard over vast distances.

S2. Ans.(b)
Sol.

Time constant of RC circuit = R_eq C_eq
Both resistance and capacitance are connected in parallel. So,
R_eq=R/2,
C_eq=2C
Hence, Net time-constant = R_eq C_eq = R/2.2C=RC

S3. Ans.(c)
Sol. In the Schottky barrier diode current flows due to majority carriers, which are electrons in an N-type semiconductor and holes in P-type semiconductor.

S4. Ans.(c)
Sol. Frequency Shift Keying (FSK) is the digital modulation technique in which the frequency of the carrier signal varies according to the digital signal changes. FSK is a scheme of Frequency Modulation.

S5. Ans (b)
Sol. Starting from Left to Right, the first bit is called as MSB (Most Significant Bit). It also represents the signed or unsigned bit.

S6. Ans.(d)
Sol. If Current is flowing inside the transistor then it is positive. To make transistor terminal current positive electrons must flow out of the transistor at the terminal
because current and electrons always flow in opposite direction.

S7. Ans.(c)
Sol. For binary division at first we will convert binary to decimal and then do further division.
Step 1: Converting binary to decimal
110002 = 2410
and, 1002 = 410
Step 2: Now dividing both, we get
24/4 = 6
Step 3: Converting back to binary number
610 = 1102

S8. Ans(b)
Sol. Pre-emphasis is the process of artificial boosting of high frequency components of m(t) to increase corresponding Signal to Noise ratio(S/N). It is used in the transmitter section before modulation using Lead Compensator. It is like High pass Filter or differentiator. It passes high frequency but with amplification. So, Pre-emphasis circuit is used before demodulation.

S9. Ans (d)
Sol. An isotropic medium is such medium in which the permittivity(ε) and permeability(μ) of the medium are uniform in all directions of the medium, for example in free space.

S10. Ans.(a)
Sol. Current equation in RL circuit is –
i(t) =V/R (1-e^(- tR/L) )
At t = ∞ steady state current is –
i (∞)=V/R (1-e^(-∞) )=V/R

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