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Which of the following four alternatives is not correct?

We need modulation 1) to increase the selectivity 2) to reduce the time lag between transmission and reception of the information signal 3)... View Article

In optical communication system operating at 1200 mm, only 2% of the source frequency is available for TV transmission having a bandwidth of 5 MHz. The number of TV channels that can he transmitted is

1) 2 million 2) 10 million 3) 0.1 million 4) 1 million 5) 0.5 million Answer: 4) 1 million Solution: The frequency for optical... View Article

A diode AM detector with the output circuit consisting of R = 1kΩ and C = 1μF would be more suitable for detecting a carrier signal of

1) 0.1 kHz 2) 0.5 kHz 3) 1 kHz 4) 0.75 kHz 5) 10 kHz Answer: 3) 1 kHz Solution: Here, R=1kΩ=103Ω... View Article

A TV tower has a height 150 m. What is the total population covered by the TV tower, if the population density around the TV tower is 10³ km^-2? The radius of the earth is 6.4 × 10⁶m.

1) 60.288 lakh 2) 40.192 lakh 3) 100 lakh 4) 20.228 lakh Answer: 1) 60.288 lakh Solution: h=150m,R=6.4×106m Average... View Article

The range of frequencies allotted for FM radio is

1) 47 to 230 kHz 2) 47 to 230 MHz 3) 470 to 960 MHz 4) 88 to 108 MHz Answer: 4) 88 to 108 MHz Solution: A maximum frequency... View Article

A signal wave of frequency 12 kHz is modulated with a carrier wave of frequency 2.51 MHz. The upper and lower sideband frequencies are respectively

1) 2512 kHz and 2508 kHz 2) 2522 kHz and 2488 kHz 3) 2502 kHz and 2498 kHz 4) 2522 kHz and 2498 kHz 5) 2512 kHz and 2488 kHz... View Article

1000 kHz carrier wave is amplitude modulated by the signal frequency 200 Hz -4000 Hz. The channel width of this case is

1) 8 kHz 2) 4 kHz 3) 7.6 kHz 4) 3.8 kHz 5) 400 kHz Answer: 1) 8 kHz Solution: Bandwidth = 2f = 2 x 4000 Hz = 8 x 103... View Article

Ozone layer blocks the radiations of wavelength

1) less than 3 × 10-7 m 2) equal to 3 × 10-7 m 3) more than 3 × 10-7 m 4) All of the above Answer: 1) less than 3... View Article

How many photons are emitted by a laser source of 5 × 10^-3 W operating at 632.2 nm in 2s?

1) 3.2 × 1016 2) 1.6 × 1016 3) 4 × 1016 4) None of these Answer: 1) 3.2 × 1016 Solution: Power of laser... View Article

What should be the minimum length of antenna for efficient transmission of signals of wavelength λ?

1) λ/2 2) λ/3 3) λ/4 4) λ/5 Answer: 3) λ/4 Solution: If the radiation and reception of the... View Article

If a radio receiver amplifies all the signal frequencies equally well, it is said to have high

1) fidelity 2) distortion 3) sensibility 4) sensitivity 5) selectivity Answer: 1) fidelity Solution The fidelity of a... View Article

In frequency modulated wave

1) frequency varies with time 2) amplitude varies with time 3) both frequency and amplitude vary with time 4) both frequency and amplitude are... View Article

The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 8.96 A when the carrier is modulated by a single sine wave. Find the percentage modulation.

1) 60.1% 2) 71 % 3) 80.1% 4) 50.1% Answer: 2) 71 % Solution: We know that (It/Ic)2=1+(m2/2) Here, It=8.96A and Ic=8A... View Article

If E_c= 20 sin 10⁵ πt and E_m= 10 sin 400 πt are carrier and modulating signals respectively, the modulation index is

1) 56% 2) 30% 3) 50% 4) 48% 5) 60% Answer: 3) 50% Solution: Modulation index = Em/Ec = 10/20 = 1/2 = 0.5 x 100 = 50%... View Article

In a video signal for transmission of the picture, what value of bandwidth is used in communication system?

1) 2.4 MHz 2) 4.2 MHz 3) 24 MHz 4) 42 MHz Answer: 2) 4.2 MHz Solution: A video signal of bandwidth 4.2 MHz is used for the... View Article

The principle of laser action involves

1) amplification of particular frequency emitted by the system 2) population inversion 3) stimulated emission 4) All of the above... View Article

In the experiment for the determination of the speed of sound in air using the resonance column method, the length of the air column that resonates in the fundamental mode, with a tuning fork is 0.1 m. When this length is changed to 0.35m, the same tuning fork resonates with the first overtone. Calculate the end correction

1) 0.012 m 2) 0.025 m 3) 0.05 m 4) 0.024 m Answer: 2) 0.025 m Solution: Let the end correction be Δl The fundamental tone for... View Article

A string of length 70 cm is stretched between two rigid supports. The resonant frequency for this string is found to be 420 Hz and 315 Hz. If there are no resonant frequencies between these two values, then what would be the minimum resonant frequency of this string?

1) 10.5 Hz 2) 1.05 Hz 3) 105 Hz 4) 1050 Hz Answer: 3) 105 Hz Solution: String fixed at both ends f = nv/2l 315 = nv/2l... View Article

Two waves are represented by y₁ = A Sin t and y₂ = A Cos t. The phase of the first wave, w.r.t. to the second wave is ………

1) more by π radian 2) less by π radian 3) more by π/2 4) less by π/2 Answer: 2) less by π radian... View Article

Consider two points lying at a distance of 10 m and 15 m from an oscillating source. If the periodic time of oscillation is 0.05 s and the velocity of wave produced is 300 m/s, then what will be the phase difference the two points?

1) π 2) π/6 3) π/3 4) 2π/3 Answer: 4) 2π/3 Solution: As velocity = v = frequency × wave length i.e. v =... View Article