Class 12 Physics Chapter 15 Communication Systems MCQs

1 Digital signals:

A deal with all sort of values

B can use decimal system

C can use binary system

D (b) and (c) both

View Answer

Answer:(b) and (c) both

2 Digital signals:

A represents values as discrete steps

B Do not represents values as discrete steps

C represent values steps

D represent random steps

View Answer

Answer:represents values as discrete steps

3 Increase in frequency deviation results into:

A increase in noise of FM receiver

B decrease in noise of AM receiver

C increase in noise of Am receiver

D decrease in noise of FM receiver

View Answer

Answer:decrease in noise of AM receiver

4 Communication channel consists of:

A transmission line only

B optical fibre only

C free space only

D All of the above

View Answer

Answer:All of the above

5 Which is more advantageous?

A analog data communication

B digital data communication

C both (a) and (b) are equally good

D depends on the situation

View Answer

Answer:digital data communication

6 A transmitting antenna at the top of a tower has a height 3200 cm and that of the receiving antenna is 5000 cm. The maximum distance between them for satisfactory communication in line of sight mode is:

(Radius of earth = 6.4 X 10⁶ m)

A 1.5 × 10³ m

B 5.5 × 10³ m

C 4.5 × 10³ m

D 4.5 × 10⁴ m

View Answer

Answer:4.5 × 10⁴ m

7 Which mode of communication is/are not employed for the transmission of T.V. signals?

A Ground wave propagation

B Sky wave propagation

C Both (a) and (b)

D None of these

View Answer

Answer:Both (a) and (b)

8 If both the length of an antenna and the wave length of the signal to be transmitted are doubled, the power radiated by the antenna

A is doubled

B is halved

C increases 16 times

D remains constant

View Answer

Answer:remains constant

9 Modulation is the process of superposing

A high frequency audio signal on low frequency audio signal

B high frequency message signal on low frequency audio waves

C low frequency message signal on high frequency waves

D low frequency radio signal on high frequency audio waves

View Answer

Answer:low frequency message signal on high frequency waves

10 A TV tower has a height of 100 m. The maximum distance upto which the T.V. Trans- mission can be received (Radius of earth = 8 X 10⁶ m)?

A 34.77 km

B 32.70 km

C 40 km

D 40.70 km

View Answer

Answer:40 km

11 Which of the following mode of propagation is used to send radio-waves from one place to another?

A Space wave propagation

B Sky wave propagation

C Ground wave propagation

D All of them

View Answer

Answer:All of them

12 The radio waves of frequency 300 MHz to 3000 MHz belong to

A High frequency band

B Ultra high frequency band

C Very high frequency band

D Super high frequency band

View Answer

Answer:Ultra high frequency band

13 12 A TV transmission tower has a height of 240 m. Signals broadcast from this tower will be received by LOS communication at a distance of (assume the radius of the earth to be 6.4 × 10⁶ m)

A 100 km

B 24 km

C 55 km

D 50 km

View Answer

Answer:B, C, D

14 Audio sine waves of 3 kHz frequency are used to amplitude modulate a carrier signal of 1.5 MHz. Which of the following statements are true?

A The sideband frequencies are 1506 kHz and 1494 kHz

B The bandwidth required for amplitude modulation is 6kHz

C The bandwidth required for amplitude modulation is 3 MHz

D The sideband frequencies are 1503 kHz and 1497 kHz.

View Answer

Answer:B, D

15 An audio signal of 15kHz frequency cannot be transmitted over long distances without modulation because

A the size of the required antenna would be at least 5 km which is not convenient

B the audio signal can not be transmitted through sky waves

C the size of the required antenna would be at least 20 km, which is not convenient

D effective power transmitted would be very low, if the size of the antenna is less than 5 km

View Answer

Answer:A, B, D

16 A message signal of frequency ωm is superposed on a carrier wave of frequency ωc to get an amplitude modulated wave (AM). The frequency of the AM wave will be

A ωm

B ωc

C ωc + ωm/2

D ωc – ωm/2

View Answer

Answer:ωc

17 A speech signal of 3 kHz is used to modulate a carrier signal of frequency 1 MHz, using amplitude modulation. The frequencies of the sidebands will be

A 1.003 MHz and 0.997 MHz

B 3001 kHz and 2997 kHz

C 1003 kHz and 1000 kHz

D 1 MHz and 0.997 MHz

View Answer

Answer:1.003 MHz and 0.997 MHz

18 A 1 KW signal is transmitted using a communication channel which provides attenuation at the rate of – 2dB per km. If the communication channel has a total length of 5 km, the power of the signal received is [gain in dB = 10 log P0/P1]

A 900 W

B 100 W

C 990 W

D 1010 W

View Answer