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: A

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: A

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: A

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: A

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: A

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: A

Question. Long distance short wave radio broadcasting uses
(a) Sky wave
(b) Direct wave
(c) Space wave
(d) Ground wave

Answer: A

Question. 3-30 MHz frequency range is known as
(a) HF
(b) VHF
(c) UHF
(d) MF

Answer: A

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: A

Question. Satellite communication is generally carried out for frequencies above
(a) 20 MHz
(b) 20 kHz
(c) 1 kHz
(d) 1 MHz

Answer: A

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: A

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: A

Question. A demodulator circuit contains
(a) A diode
(b) A transistor
(c) A solar cell
(d) Logic gate

Answer: A

Question. A device which converts one type of energy into other is known as
(a) Transducer
(b) Receiver
(c) Transmitter
(d) Attenuator

Answer: A

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: A

Question. The communication satellites are parked at an altitude of
(a) 36000 km
(b) 3600 km
(c) 360 km
(d) 36 km

Answer: A

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: A

Question. Modem is a device used for
(a) Both
(b) Modulation
(c) Demodulation
(d) None of these

Answer: A

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: A

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: A

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: A

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: A

Question. The ‘Facsimile Transmission (FAX)’ involves
(a) Exact reproduction of a document or static picture
(b) Taking photograph
(c) Speech communication
(d) Telegraphy

Answer: A

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: A

Question. Which of the following modulation index produces noise?
(a) 1.2
(b) 0.7
(c) 0.8
(d) 0.5

Answer: A

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: A

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: A

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: A

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: A

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: A

Question. Refractive index of ionosphere is
(a) Less than one
(b) One
(c) More than one
(d) Zero

Answer: A

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: A

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: A

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: A

Question. Arrange the following communication frequency bands in the increasing order of frequencies
(a) 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

Question. The waves used by artificial satellites for communication purposes are
(a) Microwaves
(b) AM radiowaves
(c) X-rays
(d) FM radiowaves

Answer: A

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: A

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: A

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: A

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: A

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: A