# CBSE Class 12 Physics HOTs Communications Systems

CBSE Class 12 Physics - COMMUNICATIONS SYSTEMS. HOTs Questions Database. Based on CBSE and NCERT guidelines. The students should practice these HOTs Questions to gain perfection which will help him to get more marks in CBSE examination. Based on CBSE and NCERT guidelines. Based on the same pattern as released by CBSE every year. CBSE releases HOTs Questions every year. These papers are released prior to the CBSE board examinations so that students can do practice. database of 1 marks, 2 marks, 3 marks and 5 marks questions. Please refer to more CBSE sample papers, question papers, HOTs etc in other links.

UNIT-10

Communications System

1) Why are micro wave used in radars?

2) Why sky waves are not used in the transmission of television signals?

3) What should be the desirable characteristic of a diode detector?

4) Give a velocity factor of a line.

5) Why is delta modulation a convenient method of digital modulation.

6) Where the two wire transmission line, Coaxial cable, Optical fiber are employed.

7) what is heterodyning?.

8) What is population inversion? How is it achieved?.

9) Enumerate the various types of Lasers?.

10)Lists some of the applications of Lasers?.

11)Name the prime elements of a telecommunications network.

12) Audio signal cannot be transmitted directly in to the space why?

13) What is pulse modulation?

14) What is precisely meant by the term channel in a communication system “?

15) Why does the electrical conductivity of earths atmosphere increase with altitude ?

16) Explain numerical aperture in fibre optical

17) Differentiate between (i) PAM and (II) PPM .

18)Why the transmission of signal is not possible for frequency greater than 20Mhz .

19)How does the effective power radiated by the antenna vary with wavelength?

20)what should be the length of the dipole antenna for a carrier wave of 5 X 10 8hz ?

21)By how much should the height of the antenna be increased to double the coverage range R= 6400 Km.

22) A TV. tower has a height of lOOm . How much population is covered by the TV. broadcaste if the average population density around the tower is 1000/km2

23)Ground receiver station is receiving a signal at (i) 5MH and (ii 100MHz transmitted from a round transmitter at a height of 300 m, located at a distance of 100 km from the receiver station. Identify whether the signal is coming via space wave or sky wave propagation or satellite transponder. Radius of earth = 6.4 x 106 m. Nmax of the Isosphere = 1012 m3

Please refer to attached file for COMMUNICATIONS SYSTEMS.

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