M.C.Q (1 Marks)

Question 11 Mark

Assertion : Microwave propagation is better than the sky wave propagation.

Reason : Microwaves have frequencies 100 to 300 GHz, which have very good directional properties.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Answer

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

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Question 21 Mark

Assertion : The television broadcasting becomes weaker with increasing distance.

Reason : The power transmitted from TV transmitter varies inversely as the distance of the receiver

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Answer

(c) If assertion is true but reason is false.

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Question 31 Mark

If f_a and f_f represent the carrier wave frequencies for amplitude and frequency modulations respectively, then

(a)

(b)

(c)

(d)

Answer

(b)

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Question 41 Mark

If m₁ and m₂ are the refractive indices of the materials of core and cladding of an optical fibre, then the loss of light due to its leakage can be minimised by having

(a) m₁ > m₂

(b) m₁ < m₂

(c) m₁ = m₂

(d) None of these

Answer

(a) m₁ > m₂

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Question 51 Mark

Assertion : The surface wave propagation is used for medium wave band and for television broadcasting.

Reason : The surface waves travel directly from transmitting antenna to receiver antenna through atmosphere.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Answer

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

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Question 61 Mark

Sinusoidal carrier voltage of frequency 1.5 MHz and amplitude 50 V is amplitude modulated by sinusoidal voltage of frequency 10 kHz producing 50% modulation. The lower and upper side-band frequencies in kHz are

(a) 1490, 1510

(b) 1510, 1490

(c)

(d)

Answer

(a) 1490, 1510

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Question 71 Mark

Assertion : Fax is a modulating and demodulating device.

Reason : It is necessary for exact reproduction of a document.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If assertion is false but reason is true.

Answer

(d) If assertion is false but reason is true.

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Question 81 Mark

Assertion : The electromagnetic waves of shorter wavelength can travel longer distances on earth's surface than those of longer wavelengths.

Reason : Shorter the wavelength, the larger is the velocity of wave propagation.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Answer

(c) If assertion is true but reason is false.

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Question 91 Mark

A 500 Hz modulating voltage fed into an FM generator produces a frequency deviation of 2.25 kHz. If amplitude of the voltage is kept constant but frequency is raised to 6 kHz then the new deviation will be

(a) 4.5 kHz

(b) 54 kHz

(c) 27 kHz

(d) 15 kHz

Answer

(b) 54 kHz

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Question 101 Mark

The modulation index of an FM carrier having a carrier swing of 200 kHz and a modulating signal 10 kHz is

(a) 5

(b) 10

(c) 20

(d) 25

Answer

(b) 10

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Question 111 Mark

Assertion : The electrical conductivity of earth's atmosphere decreases with altitude.

Reason : The high energy particles (i.e. 𝛾-rays and cosmic rays) coming from outer space and entering our earth's atmosphere cause ionisation of the atoms of the gases present there and the pressure of gases decreases with increase in altitude.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If assertion is false but reason is true.

Answer

(d) If assertion is false but reason is true.

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Question 121 Mark

In AM, the centpercent modulation is achieved when

(a) Carrier amplitude = signal amplitude	(b) Carrier amplitude ≠ signal amplitude
(c) Carrier frequency = signal frequency	(d) Carrier frequency ≠ signal frequency

Answer

(a) Carrier amplitude = signal amplitude

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Question 131 Mark

The total power content of an AM wave is 900 W. For 100% modulation, the power transmitted by each side band is

(a) 50 W

(b) 100 W

(c) 150 W

(d) 200 W

Answer

(c) 150 W

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Question 141 Mark

An amplitude modulated wave is modulated to 50%. What is the saving in power if carrier as well as one of the side bands are suppressed

(a) 70%

(b) 65.4%

(c) 94.4%

(d) 25.5%

Answer

(c) 94.4%

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Question 151 Mark

A transmitter supplies 9 kW to the aerial when unmodulated. The power radiated when modulated to 40% is

(a) 5 kW

(b) 9.72 kW

(c) 10 kW

(d) 12 kW

Answer

(b) 9.72 kW

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Question 161 Mark

The bit rate for a signal, which has a sampling rate of 8 kHz and where 16 quantisation levels have been used is

(a) 32000 bits/sec

(b) 16000 bits/sec

(c) 64000 bits/sec

(d) 72000 bits/sec

Answer

(a) 32000 bits/sec

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Question 171 Mark

Assertion : Short wave bands are used for transmission of radio waves to a large distance.

Reason : Short waves are reflected by ionosphere

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Answer

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

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Question 181 Mark

In a communication system, noise is most likely to affect the signal

(a) At the transmitter

(b) In the channel or in the transmission line

(c) In the information source

(d) At the receiver

Answer

(b) In the channel or in the transmission line

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Question 191 Mark

The antenna current of an AM transmitter is 8 A when only carrier is sent but increases to 8.96 A when the carrier is sinusoidally modulated. The percentage modulation is

(a) 50%

(b) 60%

(c) 65%

(d) 71%

Answer

(d) 71%

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Question 201 Mark

Indicate which one of the following system is digital

(a) Pulse position modulation	(b) Pulse code modulation
(c) Pulse width modulation	(d) Pulse amplitude modulation

Answer

(b) Pulse code modulation

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Question 211 Mark

While tuning in a certain broadcast station with a receiver, we are actually

(a) Varying the local oscillator frequency

(b) Varying the frequency of the radio signal to be picked up

(c) Tuning the antenna

(d) None of these

Answer

(a) Varying the local oscillator frequency

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Question 221 Mark

An antenna is a device

(a) That converts electromagnetic energy into radio frequency signal

(b) That converts radio frequency signal into electromagnetic energy

(c) That converts guided electromagnetic waves into free space electromagnetic waves and vice-versa

(d) None of these

Answer

(c) That converts guided electromagnetic waves into free space electromagnetic waves and vice-versa

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Question 231 Mark

When the modulating frequency is doubled, the modulation index is halved and the modulating voltage remains constant, the modulation system is

(a) Amplitude modulation	(b) Phase modulation
(c) Frequency modulation	(d) All of the above

Answer

(c) Frequency modulation

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Question 241 Mark

What type of modulation is employed in India for radio transmission

(a) Amplitude modulation	(b) Frequency modulation
(c) Pulse modulation	(d) None of these

Answer

(a) Amplitude modulation

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Question 251 Mark

A photodetector is made from a semiconductor In _0.53Ga _0.47As with E_g = 0.73 eV. What is the maximum wavelength, which it can detect

(a) 1000 nm

(b) 1703 nm

(c) 500 nm

(d) 173 nm

Answer

(b) 1703 nm

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Question 261 Mark

Assertion : In high latitude one sees colourful curtains of light hanging down from high altitudes.

Reason : The high energy charged particles from the sun are deflected to polar regions by the magnetic field of the earth.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Answer

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

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Question 271 Mark

Consider an optical communication system operating at l~ 800 nm. Suppose, only 1% of the optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting audio signals requiring a bandwidth of 8 kHz

(a) 4.8 × 10⁸

(b) 48

(c) 6.2 × 10⁸

(d) 4.8 × 10⁵

Answer

(a) 4.8 × 10⁸

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Question 281 Mark

In a diode AM-detector, the output circuit consist of R = 1kW and C = 10 pF. A carrier signal of 100 kHz is to be detected. Is it good

(a) Yes	(b) No
(c) Information is not sufficient	(d) None of these

Answer

(b) No

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Question 291 Mark

A sky wave with a frequency 55 MHz is incident on D-region of earth's atmosphere at 45^o. The angle of refraction is (electron density for D-region is 400 electron/cm³)

(a) 60°

(b) 45°

(c) 30°

(d) 15°

Answer

(b) 45°

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Question 301 Mark

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) ~ 10⁶ m^–3

(c) ~ 10¹⁴ m^–3

(d) ~ 10²² m^–3

Answer

(a) ~ 1.2 × 10¹² m^–3

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Question 311 Mark

Assertion : Television signals are received through sky-wave propagation.

Reason : The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Answer

(d) If the assertion and reason both are false.

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Question 321 Mark

In which of the following remote sensing technique is not used

(a) Forest density

(b) Pollution

(c) Wetland mapping

(d) Medical treatment

Answer

(d) Medical treatment

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Question 331 Mark

Audio signal cannot be transmitted because

(a) The signal has more noise

(b) The signal cannot be amplified for distance communication

(c) The transmitting antenna length is very small to design

(d) The transmitting antenna length is very large and impracticable

Answer

(d) The transmitting antenna length is very large and impracticable

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Question 341 Mark

In frequency modulation

(a) The amplitude of modulated wave varies as frequency of carrier wave

(b) The frequency of modulated wave varies as amplitude of modulating wave

(c) The amplitude of modulated wave varies as amplitude of carrier wave

(d) The frequency of modulated wave varies as frequency of modulating wave

Answer

(b) The frequency of modulated wave varies as amplitude of modulating wave

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Question 351 Mark

Advantage of optical fibre

(a) High bandwidth and EM interference

(b) Low bandwidth and EM interference

(c) High band width, low transmission capacity and no EM interference

(d) High bandwidth, high data transmission capacity and no EM interference

Answer

(d) High bandwidth, high data transmission capacity and no EM interference

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Question 361 Mark

Television signals on earth cannot be received at distances greater than 100 km from the transmission station. The reason behind this is that

(a) The receiver antenna is unable to detect the signal at a distance greater than 100 km

(b) The TV programme consists of both audio and video signals

(c) The TV signals are less powerful than radio signals

(d) The surface of earth is curved like a sphere

Answer

(d) The surface of earth is curved like a sphere

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Question 371 Mark

The phenomenon by which light travels in an optical fibres is

(a) Reflection	(b) Refraction
(c) Total internal reflection	(d) Transmission

Answer

(c) Total internal reflection

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Question 381 Mark

Consider telecommunication through optical fibres. Which of the following statements is not true

(a) Optical fibres may have homogeneous core with a suitable cladding

(b) Optical fibres can be of graded refractive index

(c) Optical fibres are subject to electromagnetic interference from outside

(d) Optical fibres have extremely low transmission loss

Answer

(c) Optical fibres are subject to electromagnetic interference from outside

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Question 391 Mark

In an FM system a 7 kHz signal modulates 108 MHz carrier so that frequency deviation is 50 kHz. The carrier swing is

(a) 7.143

(b) 8

(c) 0.71

(d) 350

Answer

(a) 7.143

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Question 401 Mark

The waves used in telecommunication are

(a) IR

(b) UV

(c) Microwave

(d) Cosmic rays

Answer

(c) Microwave

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Question 411 Mark

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

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

Answer

(c) Ultra high frequency band

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Question 421 Mark

For television broadcasting, the frequency employed is normally

(a) 30-300 MHz

(b) 30-300 GHz

(c) 30-300 KHz

(d) 30-300 Hz

Answer

(a) 30-300 MHz

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Question 431 Mark

The frequency of a FM transmitter without signal input is called

(a) Lower side band frequency	(b) Upper side band frequency
(c) Resting frequency	(d) None of these

Answer

(c) Resting frequency

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Question 441 Mark

An AM wave has 1800 watt of total power content, For 100% modulation the carrier should have power content equal to

(a) 1000 watt

(b) 1200 watt

(c) 1500 watt

(d) 1600 watt

Answer

(b) 1200 watt

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Question 451 Mark

If a number of sine waves with modulation indices n₁, n₂, n₃ ........ modulate a carrier wave, then total modulation index (n) of the wave is

(a) n₁ + n₂ .... + 2(n₁ + n₂.....)	(b)
(c)	(d) None of these

Answer

(c)

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Question 461 Mark

Which of the following is the disadvantage of FM over AM

(a) Larger band width requirement	(b) Larger noise
(c) Higher modulation power	(d) Low efficiency

Answer

(a) Larger band width requirement

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Question 471 Mark

Basically, the product modulator is

(a) An amplifier	(b) A mixer
(c) A frequency separator	(d) A phase separator

Answer

(b) A mixer

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Question 481 Mark

What is the modulation index of an over modulated wave

(a) 1

(b) Zero

(c) < 1

(d) > 1

Answer

(d) > 1

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Question 491 Mark

The maximum peak to peak voltage of an AM wire is 24 mV and the minimum peak to peak voltage is 8 mV. The modulation factor is

(a) 10%

(b) 20%

(c) 25%

(d) 50%

Answer

(d) 50%

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Question 501 Mark

An oscillator is producing FM waves of frequency 2 kHz with a variation of 10 kHz. What is the modulating index

(a) 0.20

(b) 5.0

(c) 0.67

(d) 1.5

Answer

(b) 5.0

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Physics M.C.Q (1 Marks)

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