JEE Physics Communication System MCQs Set B

Question:  An information signal of 150 MHz is to be sent across a distance of 40 km. Which mode of communication is suitable?

• a) Space wave propagation
• b) Satellite communication
• c) Ground wave propagation
• d) Sky wave propagation

Answer: Space wave propagation

Question: The communication satellite are parked at a height of (from surface of earth)

• a) 36000 km
• b) 3600 km
• c) 360 km
• d) 36 km

Answer: 36000 km

Question: For VHF television broadcasting, the frequency employed is generally

• a) 54 - 72 MHz
• b) 420 - 890 MHz
• c) 540 - 1600 kHz
• d) 88 - 108 kHz

Answer: 54 - 72 MHz

Question: Line of sight (LOS) communication is also known as

• a) Space wave communication
• b) Ionospheric communication
• c) Ground wave communication
• d) Sky wave communication

Answer: Space wave communication

Question: If a carrier of 1000 kHz is used to carry the signal, the length of transmitting antenna will be equal to

• a) 75 m
• b) 3000 mn
• c) 30 m
• d) 3 m

Answer: 75 m

Question: Modem is a device used for

• a) Either of these
• b) Converting digital to analog signals
• c) Converting analog signal to digital signals
• d) None of these

Answer: Either of these

Question: Long distance short wave radio broadcasting uses

• a) Sky wave
• b) Direct wave
• c) Space wave
• d) Ground wave

Answer: Sky wave

Question: 3-30 MHz frequency range is known as

• a) HF
• b) VHF
• c) UHF
• d) MF

Answer: HF

Question: A photodetector is made from a compound semiconductor with band gap 0.73 eV. The maximum wavelength it can detect is

• a) 17030 Å
• b) 6200 Å
• c) 1703 Å
• d) 12400 Å

Answer: 17030 Å

Question: Satellite communication is generally carried out for frequencies above

• a) 20 MHz
• b) 20 kHz
• c) 1 kHz
• d) 1 MHz

Answer: 20 MHz

More Questions..............................

Question: An AM broadcasting station has a vertical telescopic transmitting antenna and a receiver has a vertical telescopic antenna. The receiver will respond to

• a) Electric component of the electromagnetic wave produced by antenna
• b) Magnetic component of the electromagnetic wave produced by antenna
• c) Both electric and magnetic components of electromagnetic wave produced by antenna
• d) 50% of both components of electromagnetic wave produced by antenna

Answer: Electric component of the electromagnetic wave produced by antenna

Question:

• a) 20 km
• b) 40 km
• c) 10 km
• d) 1 km

Answer: 20 km

Question: An audio signal of amplitude one half the carrier amplitude is used in an amplitude modulation. The modulation index is

• a) 0.50
• b) 0.125
• c) 0.25
• d) 2

Answer: 0.50

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A demodulator circuit contains

• a) A diode
• b) A transistor
• c) A solar cell
• d) Logic gate

Answer: A diode

Question: A device which converts one type of energy into other is known as

• a) Transducer
• b) Receiver
• c) Transmitter
• d) Attenuator

Answer: Transducer

Question: On a particular day, the maximum frequency reflected from the ionosphere is 10 MHz. The maximum electron density in ionosphere is

• a) 1.23 × 10¹²/m³
• b) 1/9 × 10⁶/m³
• c) 10⁶/m²
• d) 10¹²/m³

Answer: 1.23 × 10¹²/m³

Question: Need for modulation" arises due to which of the following reasons?

• a) All of these
• b) It allows multiple user-friendly communication
• c)

  

• d)

  

Answer: All of these

Question: The area of the region covered by the T.V., broadcast by a T.V. tower of height 100 m is (in m²)

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 60°
• b) 45°
• c) 30°
• d) 15°

Answer: 60°

Question: The communication satellites are parked at an altitude of

• a) 36000 km
• b) 3600 km
• c) 360 km
• d) 36 km

Answer: 36000 km

Question: A photodetector is made of a compound semiconductor with the band gap of 0.73eV. The maximum wavelength it can detect is

• a) 17030 Å
• b) 6200 Å
• c) 1703 Å
• d) 12400 Å

Answer: 17030 Å

Question: Modem is a device used for

• a) Both
• b) Modulation
• c) Demodulation
• d) None of these

Answer: Both

Question: If a carrier wave of 1000 kHz is used to carry the signal, the length of transmitting antenna will be equal to

• a) 75 m
• b) 3000 m
• c) 30 m
• d) 3 m

Answer: 75 m

Question: A ground receiver station is receiving a signal at 100 MHz transmitted from a ground transmitter at a height of 300 m located at a distance of 1000 km. It is coming via

• a) Satellite communication
• b) Sky wave
• c) Space wave
• d) Ground wave

Answer: Satellite communication

Question: In an AM wave for audio frequency of 3400 cycle/s, the appropriate carrier frequency will be

• a) 800,000 Hz
• b) 60000 Hz
• c) 34000 MHz
• d) 1000 Hz

Answer: 800,000 Hz

Question: In frequency modulation, the amount of frequency deviation depends on the

• a) Amplitude of audio signal
• b) None of these
• c) Frequency of audio signal
• d) Both the frequency and amplitude of audio signal

Answer: Amplitude of audio signal

Question: The ‘Facsimile Transmission (FAX)’ involves

• a) Exact reproduction of a document or static picture
• b) Taking photograph
• c) Speech communication
• d) Telegraphy

Answer: Exact reproduction of a document or static picture

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A transmitting antenna at the top of tower has a height 32 m and height of receiving antenna is 50 m. Minimum distance between them for satisfactory LOS mode of communication is

• a) 45 km
• b) 60 km
• c) 100 km
• d) 40 km

Answer: 45 km

Question: Which of the following modulation index produces noise?

• a) 1.2
• b) 0.7
• c) 0.8
• d) 0.5

Answer: 1.2

Question: The radiowaves of frequency 300 MHz to 3000 MHz belong to

• a) Ultra high frequency band
• b) Super high frequency band
• c) Very high frequency band
• d) High frequency band

Answer: Ultra high frequency band

Question: Range of frequencies alotted for commerical FM radio broad cast is

• a) 88 to 108 MHz
• b) 88 to 108 kHz
• c) 8 to 88 MHz
• d) 88 to 108 GHz

Answer: 88 to 108 MHz

Question: The length of a half wave dipole antenna at 30 MHz is

• a) 5 m
• b) 100 m
• c) 50 m
• d) 10 m

Answer: 5 m

Question: In a single reflection from the ionosphere, the sky waves cover a distance on ground not more than

• a) 4000 km
• b) 400 km
• c) 4000 m
• d) 400 m

Answer: 4000 km

Question: The maximum range of ground or surface wave propagation depends on

• a) Both on frequency as well as power
• b) Wavelength of radiowaves
• c) Power of the transmitter only
• d) The frequency of radiowaves only

Answer: Both on frequency as well as power

Question: Refractive index of ionosphere is

• a) Less than one
• b) One
• c) More than one
• d) Zero

Answer: Less than one

Question: For sky wave propagation of a 10 MHz signal, what should be the minimum electron density in ionosphere?

• a) 1.2 × 10¹² m^–3
• b) 1.2 × 10¹⁴ m^–3
• c) 1.2 × 10¹⁶ m^–3
• d) 1.2 × 10⁸ m^–3

Answer: 1.2 × 10¹² m^–3

Question: The TV tower has a height of 100 m. What is the maximum distance upto which the T.V. transmission can be received ?

• a) 35.2 km
• b) 40.70 km
• c) 32.70 km
• d) 34.77 km

Answer: 35.2 km

Question: If both the length of the antenna and the wavelength of the signal to the transmitted are doubled, the power radiated by the antenna

• a) Remains constant
• b) Is doubled
• c) Is halved
• d) Increases 16 times

Answer: Remains constant

Question: Arrange the following communication frequency bands in the increasing order of frequencies

a. AM broadcast b. Cellular mobile radio c. FM broadcast d. Television UHF e. Satellite communication

• a) a, c, d, b, e
• b) e, b, d, c, a
• c) a, c, b, d, e
• d) a, b, c, d, e

Answer: a, c, d, b, e

Question: The waves used by artificial satellites for communication purposes are

• a) Microwaves
• b) AM radiowaves
• c) X-rays
• d) FM radiowaves

Answer: Microwaves

Question:

• a)

  

• b) 3r
• c) 4r
• d) 5r

Answer:

Question: Modulation is the process of superposing

• a) Low frequency audio signal on high frequency waves
• b) Low frequency radio signal on low frequency audiowaves
• c) High frequency radio signal on low frequency audio signal
• d) High frequency audio signal on low frequency radiowaves

Answer: Low frequency audio signal on high frequency waves

Question: Which range of frequencies can be transmitted suitably by sky wave propagation?

• a) 2 MHz to 20 MHz
• b) Above 50 MHz
• c) 1 MHz to 2 MHz
• d) 5 kHz to 500 kHz

Answer: 2 MHz to 20 MHz

Question: In an optical fibre, the light signal is transmitted by

• a) Repeated total internal reflections at the core and cladding interface
• b) Polarisation of optical signals
• c) Interference between the incident and inflected waves
• d) Refraction at the core-cladding interface

Answer: Repeated total internal reflections at the core and cladding interface

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The band width of amplitude modulation is

• a) Double the frequency of audio signal
• b) Double the frequency of carrier wave
• c) Equal to frequency of aduio signal
• d) Half the frequency of carrier wave

Answer: Double the frequency of audio signal

Question: Electromagnetic waves with frequencies greater than the critical frequency of ionosphere cannot be used for communication using sky wave propagation because

• a) The refractive index of ionosphere becomes very high for f > f_c
• b) The refractive index of ionosphere becomes very low for f > f_c
• c) The refractive index of ionosphere becomes very high for f < f_c
• d) The refractive index of ionosphere becomes very low for f < f_c

Answer: The refractive index of ionosphere becomes very high for f > f_c