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COMMUNICATION SYSTEM Quiz-12

As per analysis for previous years, it has been observed that students preparing for NEET find Physics out of all the sections to be complex to handle and the majority of them are not able to comprehend the reason behind it. This problem arises especially because these aspirants appearing for the examination are more inclined to have a keen interest in Biology due to their medical background. Furthermore, sections such as Physics are dominantly based on theories, laws, numerical in comparison to a section of Biology which is more of fact-based, life sciences, and includes substantial explanations. By using the table given below, you easily and directly access to the topics and respective links of MCQs. Moreover, to make learning smooth and efficient, all the questions come with their supportive solutions to make utilization of time even more productive. Students will be covered for all their studies as the topics are available from basics to even the most advanced. .

Q1. Laser beams are used to measure long distances because
•  They are monochromatic
•  They are highly polarised
•  They are coherent
•  They have high degree of parallelism
Solution
Laser beams are perfectly parallel. So that they are very narrow and can travel a long distance without spreading. This is the feature of laser while they are monochromatic and coherent these are characteristics only

Q2.The antenna current of an AM broadcast transmitter modulated by 50% is 11. Find the carrier current
•  9.25 A
•  10 A
•  10.35 A
•  5.5 A
Solution
Icarrier=Itotal/(1+ma2/2)1/2 =11/√1+(0.5)2⁄2 =10.35 A

Q3. What should be the maximum acceptance angle at the aircore interface of an optical fibre if n1and n2 are the refractive indices of the core and the cladding, respectively
•   sin-1⁡(n2/n1)
•  sin-1⁡√n12-n22
•  [tan-1⁡ n2/n1  ]
•  [tan-1⁡ n1/n2  ]
Solution
Core of acceptance angle Î¸=sin-1⁡√n12-n22

Q4. Basically, the product modulator is
•  An amplifier
•  A mixer
•  A frequency separator
•  A phase separator
Solution
It mixes weak signals with carrier signals

Q5.Mean optical power launched into an 8 km fibre is 120 Î¼W and mean output power is 4 Î¼W, then the overall attenuation is (Given log⁡ 30=1.477)
•  14.77 dB
•  16.77 dB
•  3.01 dB
•  None of these
Solution
Attenuation =10log⁡ 120/4=10 log⁡30  =10×1.4771=14.77 dB

Q6. A dim star of magnitude + 14.5 explodes into a nova a magnitude +2. The factor by which the brightness of the star has increased is
•  12.5
•  102
•  103
•  105
Solution
I1/I2 =(100)(m1-m2 )/5=(100)(14.5-2)/5=(100)5/2=105

Q7.The velocity of electromagnetic wave in good conductor is
•  3×108 ms-1
•  More than 3×108 ms-1
•  Very low
•  High
Solution
The velocity of electromagnetic waves in a conductor is given by v= 1/√Î¼0 Î¼r Îµ0 Îµr =c/√Î¼r Îµr  Since, the value of Î¼r and Îµr are greater than 1, hence v<<c

Q8.The phenomenon by which light travels in an optical fibres is
•  Reflection
•  TRefraction
•  Total internal reflection
•  Transmission
Solution
In optical fibre, light travels inside it, due to total internal reflection

Q9.The carrier frequency generated by a circuit containing 1 nF capacitor and 10 Î¼H inductor is
•  1592 Hz
•  1592 kHz
•  159.2 Hz
•  15.92 kHz
Solution
b) C=1 nF=10-9 F,L=10Î¼H=10-5
v=1/2Ï€√LC=1/2Ï€√10-5×10-9 =107/2Ï€ =1.592×104 Hz=1592 kHz

Q10. The output stage of a television transmitter is most likely to be a
•  Plate-modulated class C amplifier
•  Grid-modulated class C amplifier
•  Screen-modulated class C amplifier
• Grid-modulated class A amplifier
Solution
Because of their inherent distortion class C amplifiers are never used as audio amplifiers, but they are primarily employed in the final stage of TV transmitters. Also, owing to low efficiency off class A operations, these amplifiers are not employed where large RF (radio frequency) power is involved eg, to excite transmitting antenna. In such cases class C amplifiers are used, since a class C amplifier has a very high efficiency, it can deliver more load power. I output stage of a TV transmitter grid modulated class C amplifier is used.

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