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 signal have... View Article
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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 receiver is the... 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... 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... View Article
If Ec= 20 sin 105 πt and Em= 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 =... 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... 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... 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... 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... 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... View Article
The ratio of frequencies of two waves travelling through the same medium is 2: 5. The ratio of their wavelengths will be ………
1) 2 : 5 2) 5 : 2 3) 3 : 5 4) 5 : 3 Answer: 2) 5: 2 Solution:... View Article
From a point source, if the amplitude of waves at a distance r is A, its amplitude at a distance 2r will be
1) A 2) 2A 3) A/2 4) A/4 Answer: 3) A/2 Solution: Intensity = Power/Area = P/ 4πr2 Therefore, Intensity ∝ 1/r2... View Article
A uniform wire of length L, diameter D and density p is stretched under a tension T. The correct relation between its fundamental frequency f, the length Land the diameter D is
1) f ∝ (1/LD) 2)f ∝ (1/L√D) 3) f ∝ (1/D2) 4) f ∝ (1/LD2) Answer: 1) f ∝ (1/LD) Solution:... View Article
The angle of elevation of the top of a tower from two places situated at distances 21m. and x m. from the base of the tower are 450 and 600 respectively. What is the value of x?
(a) 7 √3 (b) 7- √3 (c) 7+ √3 (d) 14 Solution: Consider triangle ABD. tan 45 = AD/BD 1... View Article
The angles of elevation of the top of a tower standing on a horizontal plane from two points on a line passing through the foot of the tower at distances 49 m and 36 m are 430 and 470 respectively. What is the height of the tower?
(a) 40 m (b) 42 m (c) 45 m (d) 47 m Solution: Let height of the tower AB be... View Article
A person standing on the bank of a river observes that the angle subtended by a tree on the opposite bank is 600. When he retreats 20 feet from the bank, he finds the angle to be 300. The breadth of the river in feet is
(a) 15 (b) 15√3 (c) 10√3 (d) 10 Solution: Let h be the height of tree PQ and breadth of... View Article
A vertical pole consists of two parts, the lower part being one-third of the whole. At a point in the horizontal plane through the base of the pole and distance 20 meters from it, the upper part of the pole subtends an angle whose tangent is 1/2. The possible heights of the pole are
(a) 20 m and 20 3 m (b) 20 m and 60 m (c) 16 m and 48 m (d)... View Article
The maximum area of a right-angled triangle with hypotenuse h is
(a) h2/2√2 (b) h2/2 (c) h2/√2 (d) h2/4 Solution: Given that the hypotenuse of right-angled triangle is h. Let base... View Article
The distance of the point on y = x4 + 3x2 + 2x which is nearest to the line y = 2x – 1 is
(a) 2/√5 (b) √5 (c) 1/√5 (d) 5√5 Solution: Given y = x4 + 3x2 + 2x dy/dx = 4x3... View Article
