Quiz Electronics Engineering 17 Sep 2020

Quiz Electronics Engineering
Exam: NIC
Topic: Miscellaneous
Date: 17/09/2020

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

Q1. What will be the equipotential surfaces for a pair of equal and opposite line charges?
(a) Non-concentric cylinders
(b) Concentric Cylinders
(c) Spheres
(d) None of the above

Q2. Regarding charging of a capacitor which statement is false?
(a) the amount of time necessary to discharge a capacitor depends on its size and its series resistor
(b) time constant of an R-C circuit is the time required to charge the capacitor to 70.7% of the applied voltage
(c) five time-constants are necessary to charge the capacitor to 99 per cent of the applied voltage (or full charge).
(d) the value of one time constant = CR

Q3. Consider sinusoidal modulation in AM system. Assuming no overmodulation, the modulation index(ยต) when the maximum and the minimum value of the envelope, respectively, are 3 V and 1V, is
(a) 1/3
(b) 1/5
(c) 2
(d) 1/2

Q4. Which one of the following relations is not correct?
(a) f(t)๐›ฟ(0) = f(0)๐›ฟ(t)
(b) โˆซ_(-โˆž)^โˆžโ–’ใ€–f(t)ฮด(ฯ„)ใ€—dt = 1
(c) โˆซ_(-โˆž)^โˆžโ–’ฮด(ฯ„) dt = 1
(d) f(t)๐›ฟ(t – ฯ„) = f(ฯ„)๐›ฟ(t – ฯ„)

Q5. The output of an AND gate with three inputs, A, B, and C, is HIGH when ________:
(a) A = 1, B = 1, C = 0
(b) A = 0, B = 0, C = 0
(c) A = 1, B = 1, C = 1
(d) A = 1, B = 0, C = 1

Q6. In sign magnitude numbers:
(a) maximum bit 0 stands for positive numbers
(b) maximum bit always 1
(c) maximum bit 0 stands for negative numbers
(d) maximum bit 1 stands for positive numbers

Q7. Local area networks can transmit
(a) Faster than telecommunications over public telephone lines.
(b) Using twisted-pair wiring or coaxial cables
(c) Slower than telecommunications over pubic telephone lines.
(d) Both (a) and (b)

Q8. The minimum voltage along a transmission line is 260 V, while the maximum is 390 V. The SWR is
(a) 0.5
(b) 1.1
(c) 1.25
(d) 1.5

Q9. Resistance of a conductor is proportional to its
(a) length
(b) width
(c) both (a) and (b)
(d) none of these

Q10. A capacitor with no initial charge at t=โˆž acts as
(a) voltage source
(b) current source
(c) short-circuit
(d) open-circuit


S1. Ans.(a)

S2. Ans.(b)

S3. Ans.(d)
Sol. Given:
The minimum value of the envelope(Amin) = 1 V
The maximum value of the envelope(Amax) = 3 V
We know that, the modulation index is
ยต = (A_(max )- A_min)/(A_(max )+ A_min )
ยต = (3 – 1)/(3 + 1) = 2/4
โˆด ยต = 1/2

S4. Ans.(b)
Sol. โˆซ_(-โˆž)^โˆžโ–’ใ€–f(t)ฮด(ฯ„)ใ€— = 1 is not a property of a delta function.
(i) Sampling Property
f(t).๐›ฟ(t) = f(0)๐›ฟ(t)
f(t).๐›ฟ(t – a) = f(a).๐›ฟ(t – a)
(ii) Shifting Property
โˆซ_(-โˆž)^โˆžโ–’ใ€–f(t).ฮด(t)ใ€—dt = f(0)
โˆซ_(-โˆž)^โˆžโ–’ใ€–f(t).ฮด(t-a)ใ€—dt = f(a)
(iii) Scaling Property
๐›ฟ(at) = 1/|a| ๐›ฟ(t)
๐›ฟ(at ยฑ b) = 1/|a| ๐›ฟ(t ยฑ b/a)
(iv) Area under the impulse function is equal to one.
โˆซ_(-โˆž)^โˆžโ–’ใ€–ฮด(t)ใ€—dt = 1
(v) Time Reversal
๐›ฟ(-t) = ๐›ฟ(t)

S5. Ans. (c)
Sol. The output of AND gate is HIGH only when all the inputs of the AND gate is HIGH.

S6. Ans.(a)
Sol. In Sign magnitude number, if maximum bit is โ€˜1โ€™ then it indicates a negative number and if โ€˜0โ€™ then it indicates a positive number.

S7. Ans.(d)
Sol. Local area network can transmit faster than telecommunications over public telephone lines because they uses twisted pair wiring or coaxial cable. These wires have faster data transmission rate.

S8. Ans (d)
Sol. Given:
V_max = 390 V
V_min = 260 V
SWR = V_max/V_min
โ‡’ SWR = 390/260
So, SWR = 1.5

S9. Ans.(a)
Sol. Resistance of a conductor is
R=ฯ l/a
ฯ is specific resistivity
l is length of the conductor
A is cross-sectional area.

S10. Ans.(d)
Sol As there is no initial charge on the capacitor so voltage across the capacitor is zero.
We know that current flowing in the capacitor is
โ‡’ I = CdV/dt
So, I = 0
No current is flowing through the capacitor, hence it acts as an Open Circuit.

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