Physics M.C.Q (1 Marks)

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.

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.

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.

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.

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.

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

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

Assertion  : The electrical conductivity of earth's atmosphere decreases with altitude. 
Reason      :  The high energy particles (i.e. ?-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.

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

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

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%

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

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

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.

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

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%

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

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

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

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

What type of modulation is employed in India for radio transmission(a) Amplitude modulation(b) Frequency modulation(c) Pulse modulation(d) None of these

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.

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

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.

In which of the following remote sensing technique is not used(a) Forest density(b) Pollution(c) Wetland mapping(d) Medical treatment

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

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

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

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

The phenomenon by which light travels in an optical fibres is(a) Reflection(b) Refraction(c) Total internal reflection(d) Transmission

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

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

The waves used in telecommunication are (a) IR(b) UV(c) Microwave(d) Cosmic rays

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

For television broadcasting, the frequency employed is normally(a) 30-300 MHz(b) 30-300 GHz(c) 30-300 KHz(d) 30-300 Hz

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

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

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

Basically, the product modulator is (a) An amplifier(b) A mixer(c) A frequency separator(d) A phase separator

What is the modulation index of an over modulated wave(a) 1 (b) Zero(c) < 1(d) > 1

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%

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

Laser beams are used to measure long distances because (a) They are monochromatic(b) They are highly polarised(c) They are coherent(d) They have high degree of parallelism

A laser beam is used for carrying out surgery because it(a) Is highly monochromatic(b) Is highly coherent(c) Is highly directional(d) Can be sharply focussed

The attenuation in optical fibre is mainly due to(a) Absorption(b) Scattering(c) Neither absorption nor scattering(d) Both (a) and (b)

The electromagnetic waves of frequency 2 MHz to 30 MHz are (a) In ground wave propagation(b) In sky wave propagation(c) In microwave propagation(d) In satellite communication

Maximum useable frequency (MUF) in F-region layer is x, when the critical frequency is 60 MHz and the angle of incidence is 70°. Then x is (a) 150 MHz(b) 170 MHz(c) 175 MHz(d) 190 MHz

An antenna behaves as resonant circuit only when its length is

Broadcasting antennas are generally (a) Omnidirectional type(b) Vertical type(c) Horizontal type(d) None of these

The carrier frequency generated by a tank circuit containing 1 nF capacitor and 10 mH inductor is(a) 1592 Hz(b) 1592 MHz(c) 1592 kHz(d) 159.2 Hz

Through which mode of propagation, the radio waves can be sent from one place to another (a) Ground wave propagation (b) Sky wave propagation(c) Space wave propagation(d) All of them

In which frequency range, space waves are normally propagated(a) HF(b) VHF(c) UHF(d) SHF

The characteristic impedance of a coaxial cable is of the order of(a) 50 W  (b) 200 W(c) 270 W(d) None of these

A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the corecladding interface (a) 60°(b) 75°(c) 45°(d) None of these

Long distance short-wave radio broadcasting uses (a) Ground wave(b) Ionospheric wave(c) Direct wave(d) Sky wave

The process of superimposing signal frequency (i.e. audio wave) on the carrier wave is known as (a) Transmission(b) Reception(c) Modulation(d) Detection

In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be(a) 50 cycles/sec(b) 100 cycles/sec(c) 500 cycles/sec(d) 50,000 cycles/sec

AM is used for broadcasting because(a) It is more noise immune than other modulation systems(b) It requires less transmitting power compared with other systems(c) Its use avoids receiver complexity(d) No other modulation system can provide the necessary bandwidth faithful transmission

Range of frequencies allotted for commercial FM radio broadcast is (a) 88 to 108 MHz(b) 88 to 108 kHz(c) 8 to 88 MHz(d) 88 to 108 GHz

The velocity factor of a transmission line x. If dielectric constant of the medium is 2.6, the value of x is(a) 0.26(b) 0.62(c) 2.6(d) 6.2