Physics M.C.Q (1 Marks)

Assertion : Fax is a modulating and demodulating device.
Reason : It is necessary for exact reproduction of a document.

Assertion : Microwave propagation is better than the sky wave propagation.
Reason : Microwaves have frequencies 100 to 300 GHz, which have very good directional properties.

Assertion : The television broadcasting becomes weaker with increasing distance.
Reason : The power transmitted from TV transmitter varies inversely as the distance of the receiver

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.

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 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

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

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

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




 

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.

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

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.

Assertion : Television signals are received through sky-wave propagation.
Reason : The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.

In AM, the centpercent modulation is achieved when

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

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

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

Indicate which one of the following system is digital

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

An antenna is a device

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

What type of modulation is employed in India for radio transmission

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

In which of the following remote sensing technique is not used

Audio signal cannot be transmitted because

In frequency modulation

Advantage of optical fibre

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

The phenomenon by which light travels in an optical fibres is

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

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

The waves used in telecommunication are

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

For television broadcasting, the frequency employed is normally

The frequency of a FM transmitter without signal input is called

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

Which of the following is the disadvantage of FM over AM

Basically, the product modulator is

What is the modulation index of an over modulated wave

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

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

Laser beams are used to measure long distances because

A laser beam is used for carrying out surgery because it

The attenuation in optical fibre is mainly due to

The electromagnetic waves of frequency 2 MHz to 30 MHz are

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

An antenna behaves as resonant circuit only when its length is

Broadcasting antennas are generally

The carrier frequency generated by a tank circuit containing 1 nF capacitor and 10 mH inductor is

Through which mode of propagation, the radio waves can be sent from one place to another

In which frequency range, space waves are normally propagated

The characteristic impedance of a coaxial cable is of the order of

A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the corecladding interface

Long distance short-wave radio broadcasting uses

The process of superimposing signal frequency (i.e. audio wave) on the carrier wave is known as

In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be

AM is used for broadcasting because

Range of frequencies allotted for commercial FM radio broadcast is

The velocity factor of a transmission line x. If dielectric constant of the medium is 2.6, the value of x is