Practice Test


1) Pick out the longest wavelength from the following types of radiations


2) What should be height of transmitting antenna if the T.V. telecast is to cover a radius of 128 km ?


3) The displacement current flows in the dielectric of a capacitor when the potential difference across its plates


4) Displacement current is continuous


5) Kenneley's Heaviside layer lies between


6) In an amplitude modulated wave for audio - frequency of 500 cycles/second, the appropriate carrier frequency will be


7) Range of frequencies allotted for commercial FM radio broadcast is


8) In AM systems, complete information is conveyed by transmitting in


9) What is the minimum number of geostationary satellites required for uninterrupted global average ?


10) In which frequency range, space waves are normally propagated


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


12) For television broadcasting, the frequency employed is normally


13) An antenna behaves as a resonant circuit only when its length is


14) The attenuation in optical fibre is mainly due to


15) The maximum electric field is


16) The average energy density is


17) At an instant when the magnetic field is along the y-axis, the electric field will be along


18) Light is an electromagnetic wave. Its speed in vacuum is given by the expression


19) If magnetic monopoles existed, then which of the following Maxwell's equations would be modified ?


20) The number of wavelengths, in the visible spectrum is


21) Which of the following electromagnetic radiations have the smallest wavelength ?


22) An electromagnetic radiation has an energy 14.4 keV. To which region of electromagnetic spectrum does it belong ?


23) The area to be covered for T.V. telecast is doubled. Then the height of transmitting antenna ( T.V. tower ) will have to be


24) The frequency from 3 to 30 MHz is known as


25) Which of the following represents an infrared wavelength ?


26) In FM, modulation is doubled. This is possible if frequency deviation is


27) Radio waves of constant amplitude can be generated with


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


29) A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the core - cladding interface ?


30) Broadcasting antennas are generally


31) The radiowaves of frequency 300 MHz to 3000 MHz belong to


32) The electromagnetic waves of frequency 2 MHz to 30 MHz are


33) The maximum range of ground or surface wave propagation depends on


34) The maximum magnetic field is


35) The maximum electric force on the electron is


36) The maximum magnetic force on the electron is


37) The curve drawn between velocity and frequency of a photon in vacuum will be


38) Velocity of Electromagnetic Waves in a medium depends upon


39) Clouds are contained in a layer from the earth’s surface, which is called


40) Molybdenum is used as a target element for the production of X-rays because it is


41) A radiation of 200 W is incident on a surface which is 60% reflecting and 40% absorbing. The total force on the surface is


42) According to Maxwell’s hypothesis, changing electric field gives rise to


43) Ozone layer blocks the radiations of wavelength


44) The Electromagnetic theory of light failed to explain


45) A layer of ionosphere does not reflect waves with frequencies greater than 10 MHz; then maximum electron density in this layer is


46) X-rays are produced by jumping of


47) The density of air at the top of mesosphere in comparison to that of near the earth’s surface is


48) The wavelength of infrared rays is of the order of


49) The speed of electromagnetic Wave in vacuum depends upon the source radiation. It


50) Consider the following two statements regarding a linearly polarized plane electromagnetic wave
(i)Electric field and the magnetic field have equal average values
(ii)Electric energy and the magnetic energy have equal average values


51) The temperature variation in the region of stratosphere lies from


52) Radio wave diffract around building although light waves do not. The reason is that radio waves


53) The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to


54) The magnetic field between the plate of a capacitor where r>R is given by (where r is the distance from the axis of plates and R is the radius of each plate of capacitor)


55) A radar sends the waves towards a distant object and receives the signal reflected by object. These waves are


56) Which of the following rays is emitted by a human body?


57) Which of the following relation is correct?


58) The frequency 1057 MHz of radiation arising from two close energy levels in hydrogen belongs to


59) X-ray are not used for radar purpose, because they are not


60) If alpha, beta and gamma rays carry same momentum, which has the longest wavelength?


61) If the earth did not have atmosphere, its surface temperature on a day time would be


62) Which is having minimum wavelength?


63) Which of the following shows green house effect?


64) A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields E and B with a velocity v perpendicular to both E and B, and comes out without any change in magnitude or direction of v. Then


65) An electromagnetic radiation has an energy of 13.2 keV. Then the radiation belongs to the region of


66) Out of the following electromagnetic radiation, which has the shortest wavelength?


67) The fact that radiosignals reach the earth from outside the atmosphere, was discovered accidently by


68) The ozone layer of the atmosphere lies in the region called


69) Maxwell in his famous equation of electromagnetism introduced the concept


70) The relation between electric field vector E, the displacement vector D and the polarization vector P for a dielectric placed in electric field E is given by


71) Electromagnetic Waves can be deflected by


72) Electric fields induced by changing magnetic fields are


73) The correct sequence of the increasing wavelength of the given radiation sources is


74) Maxwell in his famous equation of electromagnetism introduced the concept of


75) A lasser beam is sent to the moon and reflected back to earth by ay mirror placed on the moon by an astronaut. If the moon is 384000 km from earth, how long does it take the light to make the round trip?


76) The energy of X-ray photon is 2200 eV. Its frequency would be


77) According to Maxwell’s hypothesis, a changing electric field gives rise to


78) The shortest wavelength of X-rays emitted from an X-rays tube depends upon


79) Hydrogen atom does not emit X-rays because


80) The waves which have revolutionized telecommunication in more recent time, are


81) The wave of wavelength 5900 Å emitted by any atom or molecule must have some finite total length which is known as the coherence length. For sodium light, this length is 2.4 cm. The number of oscillations in this length will be


82) The magnetic field between the plates of radius 12 cm separated by distance of 4 mm of a parallel plate capacitor of capacitance 100 pF along the axis of plates having conduction current of 0.15 A is


83) According to Maxwell’s equation the velocity of light in any medium is expressed as


84) Height h of transmitter antenna when R is radius of earth to have range d is


85) The voltage applied across an X-ray tube is nearly equal to


86) An Electromagnetic Wave has


87) The waves which are reflected back to the earth by ionosphere is


88) A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is


89) In an Electromagnetic Wave, direction of propagation is in the direction of


90) A point source of electromagnetic radiation has an average power output of 800 W. The maximum value of electric filed at a distance 4.0 m from the source is


91) The oscillating electric and magnetic field vectors of electromagnetic wave are oriented along


92) The electric field for a plane electromagnetic wave travelling in the positive z-direction is represented by which one of the following?


93) Television signals reach us only through the ground waves. The range R related with the transmitter height h is in proportion to


94) Solar radiation is


95) Instantaneous displacement current of 1.0 A in the space between the parallel plate of 1 μF capacitor can be estabilished by changing potential difference of


96) Ground waves have wavelength


97) The wavelength of X-rays lies between


98) Which of the following is absorbed by the ozone layer?


99) The small ozone layer on top of the atmosphere is crucial for human survival because it


100) The atmosphere above the height of 80 km is called


101) The atmosphere between the heights of 50 km and 80 km is called


102) If a free electron is placed in the path of a plane electromagnetic wave, it will start moving along


103) Infrared radiation is detected by


104) All components of the Electromagnetic Spectrum in vacuum have the same


105) A. The wavelength of microwaves is greater than that of UV-rays.
B. The wavelength of IR rays is lesser than that of UV-rays.
C. The wavelength of microwaves is lesser than that of IR-rays.
D. Gamma rays have shortest wavelength in the Electromagnetic Spectrum.
Of the above statements


106) The ozone layer absorbs


107) Which of the following has zero average value in a plane electromagnetic wave?


108) Which of the following electromagnetic waves have the longest wavelength?


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


110) The principle of laser action involves


111) The modulation technique used for transforming digital data into analog signals are


112) A laser device produces amplification in the


113) Broadcasting antennas are generally


114) Fading is the variation in the strength of a signal at a receiver due to


115) Which one of the following is incorrect statement in the transmission of electromagnetic waves?


116) Because of tilting which waves finally disappear


117) Faintest stars are called


118) A geo-synchronous satellite is


119) If the area to be covered for TV telecast is doubled, then height of transmitting antenna (TV tower) will have to be


120) A transmitter transmits the message in original


121) In satellite communication, the communication satellite;


122) The galaxy in which we live is


123) In which frequencies range space waves normally propagated


124) A microphone converts


125) The modulation in which pulse duration varies in accordance with the modulating signal is called


126) If a radio receiver amplifies all the signal frequencies equally well, it is said to have high


127) Modulation is the phenomenon of


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


129) The population inversion necessary for laser action used in solid state lasers is


130) Major parts of a communication system are


131) Numerical aperture of optical fiber is a measure of


132) Primary constant of a transmission line are


133) In frequency modulated wave


134) Long distance short-wave radio broadcasting uses


135) An antenna is a device


136) The space wave propagation is utilized in


137) Which of the following is correct?


138) Audio signal cannot be transmitted because


139) Antenna is


140) In pulse modulation of analog signals, common pulse system employed are


141) Which of the following is not the main characteristic of laser beam?


142) A laser beam is used for carrying out surgery because it


143) A receiver reconstructs the original message after propagation through the channel.


144) The frequency of a FM transmitter without signal input is called


145) Ozone layer above earth's atmosphere will not


146) A signal emitted by an antenna from a certain point can be received at another point of the surface in the form of


147) The losses in transmission lines are


148) Which of the following is the disadvantage of FM over AM


149) Advantage of optical fibre is


150) Basically, a communication system is a


151) When electromagnetic waves enter the ionised layer of ionosphere, then the relative permittivity
ie,dielectric constant dielectric constant of the ionised layer


152) Laser beams are used to measure long distances because


153) Basically, the product modulator is


154) The phenomenon by which light travels in an optical fibres is


155) The output stage of a television transmitter is most likely to be a


156) Small vales of numerical aperture (NA) decrease the pulse dispersion but increase losses due to


157) A modem is a


158) Optical fibre works on the principle of


159) Large band width for higher data rate is achieved by using


160) Venus looks brighter than other stars, due to


161) The SKIP ZONE in Radio Wave Transmission is that range where


162) Which is more advantageous?


163) Which one of the following is a full duplex transmission system?


164) A laser is a coherent source because it contains


165) In amplitude modulation, carrier wave frequencies are


166) The population inversion in helium-neon laser is produced by


167) The closed structure of co-axial cable prevents inner copper wire or core or from radiating signal power. The statement is


168) Of the following which is preferred modulation scheme for digital communication


169) In ruby laser, the stimulated emission is due to transition from


170) A laser beam is used for locating distant objects because


171) The principle used in the transmission of signal through an optical fibre is


172) Which fibers are less expensive and simple to construct?


173) Intelsat satellite is used for


174) In the communication systems, AM is used for broadcasting because


175) The special theory of relativity is based on the frame of reference which has constant?


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


177) Optical fiber communication is generally preferred over general communication system because


178) In space communication, the sound waves can be sent from one place to another


179) In frequency modulation


180) The highest frequency of radiowaves which when sent at some angle towards the ionosphere, gets reflected from that and returns to the earth is called


181) The main objective of an optical source is


182) The range of frequencies allotted for FM radio is


183) The transmission media can be


184) A communication between a fixed base station and several mobile units, located on ships or aircraft utilising two way radio communication in the VHF and UHF is of frequency band


185) Point to point communication requires the use of


186) What type of modulation is employed in India for radio transmission


187) The layer of earth's atmosphere responsible for absorbing a large portion of ultraviolet radiations by the sun is


188) Which of the following device is fully duplex


189) Special theory of relativity states that


190) Modulation is the process of superposing


191) In which of the following remote sensing technique is not used


192) The electromagnetic waves of frequency 2 MHz to 30 MHz are used


193) The frequency band used in the downlink of satellite communication is


194) The attenuation in optical fibre is mainly due to


195) Present day communication systems are


196) Flash spectrum confirms a/an


197) Which of the following four alternatives is not correct? We need modulation


198) For maximum power transfer to the load, impedance of the detecting device must be equal to characteristic impedance of the transmission line


199) Quality of transmission depends only


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


201) In co-axial cable the material used as spacer is


202) The modulation technique used for transforming digital data into analog signals are


203) The principle of laser action involves


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


205) What is the range of the characteristic impedance of a coaxial cable?


206) The velocity of electromagnetic waves in a dielectric medium of constant 4 is


207) Identify the incorrect statement from the following


208) The velocity of a particle at which the kinetic energy is equal to its rest energy is


209) The difference in the refractive index of the fiber core and fiber cladding in step-index fibers is typically


210) In amplitude modulation, the bandwidth is


211) Consider telecommunication through optical fibres. Which of the following statements is no true?


212) Which of the following explain that all galaxies are receding from us?


213) Monochromatic light of wavelength 667 nm is produced by a helium neon laser. The power emitted is 9 mW. The number of photons arriving per sec. on the average at a target irradiated by this beam is


214) An optical fiber made of glass with a core of refractive index of 1.55 and include with another glass with a refractive index of 1.51. Launching takes place from air. What is the value of critical angle for core-clad boundary?


215) The modulation index of a FM signal is 0.25. If modulating frequency is 2kHz, the maximum derivative in frequency would be


216) The resistance of copper wire of diameter=2 mm is of the order of


217) A 1000kHz carrier wave is modulated by audio signal of frequency range 100-5000Hz. Then the width of the channel in kHz is


218) Frequency range for microwaves is


219) If an electromagnetic wave is transmitted to the height equal to 150 km with maximum frequency 300 kHz and critical frequency 100 kHz, the skip distance is


220) The waves relevant to telecommunications are


221) 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


222) The length of a half wave dipole at 30 MHz is


223) In space communication, the information can be passed from one place to another at a distance of 100 km in


224) A radio station has two channels. One is AM at 1020 kHz and the other FM at 89.5 Mhz For good results you will use


225) A carrier is simultaneously modulated by two sine waves having modulation indices of 0.3 and 0.4. The total modulation index will be


226) A transmitting antenna of height h and the receiving antenna of height 45 m are separated by a distance of 40 km for satisfactory communication in line of sight mode. Then the value of h is


227) What is the minimum length of antenna required to transmit a radio signal of frequency 20 MHz?


228) The glass of optical fiber has refractive index 1.55 and is clad with another glass of refractive index 1.51. When the surrounding is air, the numerical aperture will be


229) Which of the following statements is wrong?


230) For a body moving with relativistic speed, if the velocity is doubled, then


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


232) Range of frequencies allotted for commercial UHF TV broadcast is


233) What fraction of the surface area of earth can be covered to establish communication by one geostationary satellite?


234) A carrier frequency of 1MHz and peak value of 10V is amplitude modulated with a signal frequency of 10 kHz with peak value of 0.5 V. Then the modulation index and the side band frequencies respectively are


235) When radio waves passes through ionosphere, phase difference between space current and capacitive displacement current is


236) In optical communication system operating at 1200 nm, only 2% of the source frequency is available for TV transmission having a bandwidth of 5 MHz. The number of TV channels that can be transmitted is


237) In satellite communication
1. The frequency used lies between 5 MHz and 10 MHz
2. The uplink and downlink frequencies are different.
3. The orbit of geostationary satellite lies in the equatorial plane at an inclination of 0°.
In the above statements


238) 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


239) The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 8.93 A when the carrier is modulated by single sine wave. Find the percentage modulation.


240) The diameter of an optical fiber is


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


242) The cladding material of optical fibre has refractive index


243) Two electrons are moving in opposite direction with speeds 0.8 c and 0.4 c, where c the speed of light in vacuum. Then the relative speed is about


244) According o Hubble’s law the red-shift (Z) of a receding galaxy and its distance r from earth are related as


245) Which of the following frequencies will be suitable for beyond the horizon communication


246) An antenna is of height 500 m. What will be its range (Radius of earth is 6400 km)?


247) The antenna current of an AM broadcast transmitter modulated by 50% is 11. Find the carrier current


248) What should be the maximum acceptance angle at the aircore interface of an optical fibre if n1 and n2 are the refractive indices of the core and the cladding, respectively


249) A dim star of magnitude + 14.5 explodes into a nova a magnitude +2. The factor by which the brightness of the star has increased is


250) The velocity of electromagnetic wave in good conductor is


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


252) A broken ligament is being ‘welded’ back in place using 20 ms pulses from a 0.5 W laser operating at a wavelength of 632 nm. The number of photons in 5 pulses of laser are


253) Ozone layer blocks the radiations of wavelength


254) Which one of the following statements is wrong?


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


256) If sky wave with frequency of 50 MHz is incident on D region at an angle of 30°, then angle of refraction is


257) When the modulation percentage is 75, an AM transmitter produces 10 kW. How much of this is carrier power?


258) To cover a population of 20 lakh, a transmission tower should have a height … (Radius of earth = 6400 km, population per square km =1000)


259) A sky wave with a frequency 55 MHz is incident on the D-region of earth's atmosphere at30°. The angle of refraction is (electron density for D-region is 400 electron/cc)


260) The fundamental radio antenna is a metal rod which has a length equal to


261) Let A = light obtained by stimulated emission and B = light obtained by spontaneous, then


262) 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


263) In earth's atmosphere, for F1-layer; the virtual height and critical frequency are


264) A signal wave of frequency 12 kHz is modulated with a carrier wave of frequency 2.51 MHz. The upper and lower side band frequencies are respectively


265) The K line of singly ionized calcium has a wavelength of 393.3 nm as measured on earth. In the spectrum of one of the observed galaxies, this spectral line is located at 401.8 nm. The speed with which the galaxy is moving away from us, will be


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


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


268) 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


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


270) 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


271) The distance of coverage of a transmitting antenna is 12.8 km. Then, the height of the antenna is (Given that radius of earth = 6400 km)


272) A telephone link operating at a central frequency of 10 GHz is established. If 1% of this available then how many telephone channels can be simultaneously given when each telephone covering a band width of 5 kHz


273) Arrange the following communication frequency bands in the increasing order of frequencies 1. AM broadcast
2. Cellular mobile radio
3. F.M. broadcast
4. Television UHF
5. Satellite communication


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


275) For good demodulation of AM signal of carrier frequency f, the value of RC should be


276) The wavelength of red light from He-Ne laser is 633 nm in air but 474 nm in the aqueous humor inside the eye ball. Then the speed of red light through the aqueous humor is


277) The sky wave propagation is suitable for radio-waves of frequency


278) For sky wave propagation of 10 MHz signal, what should be the minimum electron density in ionosphere?


279) The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 8.93 A when the carrier is sinusoidal modulated. The percentage modulation is nearly


280) What is the value of frequency at which electromagnetic wave must be propagated for the D-region of atmosphere to have a refractive index of 0.5. Electron density for D-region is 400 electrons/cc


281) Which frequency range is used for optical communication?


282) A TV tower has a height of 75 m. What is the maximum area upto which this TV communication can be possible?


283) If both the length of an antenna and the wavelength of the signal to be transmitted are doubled, the power radiated by the antenna


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


285) What is the modulation index of an over modulated wave


286) In AM, the centpercent modulation is achieved when


287) What should be the velocity of an object so that it’s mass becomes twice of its rest mass?


288) An antenna behaves as resonant circuit only when its length is


289) 1000 kHz carrier wave is amplitude modulated by the signal frequency 200-4000 Hz. The channel width of this case is


290) The range of characteristics impedance for co-axial wire lines is


291) If the maximum amplitude of an amplitude modulated wave is 25 V and the minimum amplitude is 5 V, the modulation index is


292) What happens inside optical fibre?


293) With reference to ionospheric propogation, an electromagnetic wave with a critical frequency of 15 MHz and incident at an angle of 45° will have MUF of


294) The velocity factor of a transmission line is related to dielectric constant K of the medium is


295) Day time ionosphere comprises of


296) The transmission of high frequencies in a coaxial cable is determined by


297) The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to