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MCQOPTIONS
This section includes 1362 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 201. |
If sound intensity is 8 W/m², the dB level of this sound is about |
| A. | 5 dB |
| B. | 50 dB |
| C. | 129 dB |
| D. | 1290 dB |
| Answer» D. 1290 dB | |
| 202. |
The Nyquist sampling interval, for the signal sin c (700t) + sin c (5000 t) is |
| A. | 1/350 sec |
| B. | π/350 sec |
| C. | 1/700 sec |
| D. | π/175 sec |
| Answer» D. π/175 sec | |
| 203. |
Consider the following statements 1. In a pulsed radar, the transmitted pulses are of high frequency2. In a pulsed radar, the transmitted pulses are of high power3. In a pulsed radar, the transmitted pulses are of brief duration4. In a pulsed radar, the transmitted pulses are of square wave shape. Of the above statements the correct statements are |
| A. | 1 only |
| B. | 1, 2 and 3 only |
| C. | 1, 2, 3, 4 |
| D. | 1 and 3 only |
| Answer» C. 1, 2, 3, 4 | |
| 204. |
In an AM wave with m = 1, the carrier is suppressed. The resulting power saving will be |
| A. | 1/3 |
| B. | 1/2 |
| C. | 2/3 |
| D. | 3/4 |
| Answer» D. 3/4 | |
| 205. |
Which of the following is correct (fm is maximum usable frequency, S is speed and G is width of air gap)? |
| A. | fm = (S) (2G) |
| B. | fm = S / 2G |
| C. | fm = S / G |
| D. | G = (fm)(S) |
| Answer» D. G = (fm)(S) | |
| 206. |
If e = 10 sin(10⁸ t + 3 sin 10⁴ t) then the deviation is |
| A. | 4.77 kHz |
| B. | 47.7 kHz |
| C. | 477 kHz |
| D. | 4770 kHz |
| Answer» C. 477 kHz | |
| 207. |
Which of the following statements is correct? |
| A. | Convex lens has positive focal power and concave lens have negative focal power |
| B. | Convex lens has negative focal power and concave lens have positive focal power |
| C. | All lens have positive focal power |
| D. | All lens have negative focal power |
| Answer» B. Convex lens has negative focal power and concave lens have positive focal power | |
| 208. |
The relation between bandwidth B, modulating frequency fm and frequency deviation Δf for a sinusoidally modulated FM signal is |
| A. | B = Δf + fm |
| B. | B = 2(Δf + fm) |
| C. | B = fm - Δf/ |
| D. | B = 2(fm - Δf) |
| Answer» C. B = fm - Δf/ | |
| 209. |
A TV receiver has 20 kV EHT supply and total beam current (for 3 electron guns) of 1500 μA. The power handled by IHVT is |
| A. | 3 W |
| B. | 30 W |
| C. | 300 W |
| D. | 0.3 W |
| Answer» C. 300 W | |
| 210. |
Each of the following equation expressing decibel gain is correct except |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 211. |
If carrier power is P and amplitude modulation index is m, the total power after modulation is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» E. | |
| 212. |
Efficiency of general AM signal with em = E₁ cos ω₁t + E₂ cos ω₂ tj ec = Ec cos ωct; E₁ cos ω₁t with modulation index m₂ is __________ . |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 213. |
If the transmitted pulse power of a radar is Pt (peak value) and the antenna is isotropic, the power density at a distance r is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 214. |
A single tone modulating signal Vm cos ωt modulates a carrier A cos ωct. The carrier power (modulated) and side band powers are respectively |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 215. |
If Vs is signal voltage, Vn is noise voltage, signal to noise ratio S/N is defined as |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 216. |
Noise figure is defined as |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 217. |
The PDF of a Gaussian random variable X is given by following equation. The probability of the event {X = 4} is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 218. |
The power density spectrum of noise voltage at the input of a network is Sni and that at the output of the network is Sno. If transfer function of network is H(ω), the corresponding noise figure is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 219. |
If F(ω) is Fourier transform of f(t), then Fourier transform of f(t) cos² ωct is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 220. |
On a smooth surface, the line of sight distance between transmitting antenna (height ht metres) and receiving antenna (height hr metres) is about |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» E. | |
| 221. |
The figure shows a simple detector circuit for amplitude modulated wave v(t) = (1 + m cos ωmt) cost ωct. If the detector is to follow the envelope of modulated wave at all times the extent of modulation m must be less than or equal to m0 where m0 is given by equation |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 222. |
Waves travel on each of the line configurations in figure. In which case would the radiation be maximum |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» E. | |
| 223. |
If Pk be the probability of the message to be received or transmitted, then the amount of information (Ik) associated, in bits, will be |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» E. | |
| 224. |
The ratio given by below equation for 100% amplitude modulation with identical total transmitted power (mf is modulation index of FM) is |
| A. | 9/2 mf² |
| B. | 3/2 m²f |
| C. | 3/2 mf³ |
| D. | 9/2 m³f |
| Answer» C. 3/2 mf³ | |
| 225. |
If C is capacity of noisy channel, (bits/s), δf is bandwidth Hz and S/N is signal to noise ratio, then |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 226. |
In the figure m(t) = 2 Sin2πt / t, s(t) = cos200πt, n(t) = sin199πt / t, the output y(t) will be |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 227. |
In the following equation of M-ary PSK signal (where Ey is symbol energy), M becomes large. Then d will approach |
| A. | 2 |
| B. | infinity |
| C. | zero |
| D. | 1 |
| Answer» D. 1 | |
| 228. |
Full duplex operation permits transmission in both directions at the same time. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 229. |
In Modulation, “carrier” is |
| A. | Resultant wave |
| B. | Speech voltage to be transmitted |
| C. | Voltage with constant frequency, phase or amplitude |
| D. | Voltage for which frequency, phase or amplitude is varied |
| Answer» E. | |
| 230. |
Assertion (A): In FM the frequency of the carrier is varied by the modulating voltageReason (R): FM and PM are two forms of angle modulation. |
| A. | Both A and R are correct and R is correct explanation of A |
| B. | Both A and R are correct but R is not correct explanation of A |
| C. | A is correct but R is wrong |
| D. | A is wrong but R is correct |
| Answer» C. A is correct but R is wrong | |
| 231. |
In single tone AM modulation, the transmission efficiency for m = 1 is |
| A. | 1 |
| B. | 0.1665 |
| Answer» B. 0.1665 | |
| 232. |
A device has two resistances 300 Ω and 200 Ω respectively. The noise voltages due to these two resistance calculated separately are 5.38 μV and 4.38 μV respectively. When both of them are used together, the noise voltage will be |
| A. | 9.76 V |
| B. | 1 μV |
| C. | 23.56 μV |
| D. | 6.94 μV |
| Answer» E. | |
| 233. |
The number of spectral component of a cosine wave is |
| A. | 1 |
| B. | 0 |
| C. | 2 |
| D. | 4 |
| Answer» D. 4 | |
| 234. |
24 telephone channels are frequency division multiplexed using an SSB modulation. Assuming 3 kHz per channel, the required band width is |
| A. | 8 kHz |
| B. | 27 kHz |
| C. | 21 kHz |
| D. | 72 kHz |
| Answer» E. | |
| 235. |
Generally a VCR has |
| A. | four stationary video heads |
| B. | two stationary video heads |
| C. | four rotating video heads |
| D. | two rotating video heads |
| Answer» E. | |
| 236. |
A lens has a hyperfocal distance of 7.5 m. It is focused at 7.5 m. Then |
| A. | all objects from 7.5 m to infinity will appear in focus |
| B. | all objects from 3.75 m to infinity will appear in focus |
| C. | all objects from 0 to 7.5 m will appear in focus |
| D. | all objects from 0 to 3.75 m will appear in focus |
| Answer» C. all objects from 0 to 7.5 m will appear in focus | |
| 237. |
The dc voltage on plate modulated class C amplifier is 8 kV. If the peak modulating voltage is 4 kV, the peak RF voltage delivered to load is |
| A. | 32 kV |
| B. | 12 kV |
| C. | 0.5 kV |
| D. | 24 kV |
| Answer» E. | |
| 238. |
A linear diode detector uses RC filter. As modulation index increases the maximum permissible value of time constant RC |
| A. | increases |
| B. | decreases |
| C. | remains constant |
| D. | either (a) or (c) |
| Answer» C. remains constant | |
| 239. |
A resistor of 10 kΩ has an rms noise voltage of 1 mV under a certain set of conditions. A resistor of 20 kΩ under the same conditions will have an rms noise voltage of |
| A. | 1 mV |
| B. | 2 mV |
| C. | 1.414 mV |
| D. | 4 mV |
| Answer» D. 4 mV | |
| 240. |
Maximum undistorted power output of a transmitter is obtained when its modulation is __________ percent. |
| A. | less than 100 |
| B. | 50 |
| Answer» C. | |
| 241. |
The frequency at which the piezoelectric effect occurs is primarily determined by |
| A. | the weight of the crystal |
| B. | thickness of the crystal |
| C. | length of the crystal |
| D. | gain structure of the crystal |
| Answer» C. length of the crystal | |
| 242. |
The modulation index is, if fm = 500 Hz, Δf = 2.25 kHz |
| A. | 2.25 |
| B. | 4.5 |
| C. | 9 |
| D. | 18 |
| Answer» C. 9 | |
| 243. |
What is the frequency of the modulated carrier wave? |
| A. | 1000 Hz |
| B. | 2000 Hz |
| C. | 1000 kHz |
| D. | 2000 kHz |
| Answer» E. | |
| 244. |
The maximum distance between television transmission and receiving antennas for reasonably good reception should be |
| A. | less than 500 km |
| B. | less than 1000 km |
| Answer» C. | |
| 245. |
A sequence x(n) with the z transform X(z) = z4 + z2 - 2z + 2 - 3z - 4 is applied as an input to a linear, time invariant system with the impulse response h(n) = 2δ(n - 3) where The output at n = 4 is |
| A. | -6 |
| B. | zero |
| C. | 2 |
| D. | -4 |
| Answer» C. 2 | |
| 246. |
The disadvantage of FM over AM is that |
| A. | high output power is needed |
| B. | high modulating power is needed |
| C. | noise is very high for high frequency |
| D. | large bandwidth is required |
| Answer» E. | |
| 247. |
In equally tampered musical scale, an octave is divided into |
| A. | 12 intervals |
| B. | 10 intervals |
| C. | 7 intervals |
| D. | 5 intervals |
| Answer» B. 10 intervals | |
| 248. |
The HV supply to a TV receiver is 25 kV and the total beam current for the three electron guns is 2000 μA. The power handled by IHVT is |
| A. | 5W |
| B. | 0.5 W |
| C. | 50 W |
| D. | 500 W |
| Answer» D. 500 W | |
| 249. |
The VLF, LF and MF antennas are |
| A. | horizontally polarized |
| B. | vertically polarized |
| C. | non linearly polarized |
| D. | either (a) or (b) |
| Answer» C. non linearly polarized | |
| 250. |
In communication receivers the fidelity is provided by |
| A. | audio stage |
| B. | detector range |
| C. | mixer stage |
| D. | all of the above |
| Answer» B. detector range | |