Practice Test


Q1) Pick out the longest wavelength from the following types of radiations Show Answer


Q2) What should be height of transmitting antenna if the T.V. telecast is to cover a radius of 128 km ? Show Answer


Q3) The displacement current flows in the dielectric of a capacitor when the potential difference across its plates Show Answer


Q4) Displacement current is continuous Show Answer


Q5) Kenneley's Heaviside layer lies between Show Answer


Q6) In an amplitude modulated wave for audio - frequency of 500 cycles/second, the appropriate carrier frequency will be Show Answer


Q7) Range of frequencies allotted for commercial FM radio broadcast is Show Answer


Q8) In AM systems, complete information is conveyed by transmitting in Show Answer


Q9) What is the minimum number of geostationary satellites required for uninterrupted global average ? Show Answer


Q10) In which frequency range, space waves are normally propagated Show Answer


Q11) Through which mode of propagation, the radio waves can be sent from one place to another. Show Answer


Q12) For television broadcasting, the frequency employed is normally Show Answer


Q13) An antenna behaves as a resonant circuit only when its length is Show Answer


Q14) The attenuation in optical fibre is mainly due to Show Answer


Q15) The maximum electric field is Show Answer


Q16) The average energy density is Show Answer


Q17) At an instant when the magnetic field is along the y-axis, the electric field will be along Show Answer


Q18) Light is an electromagnetic wave. Its speed in vacuum is given by the expression Show Answer


Q19) If magnetic monopoles existed, then which of the following Maxwell's equations would be modified ? Show Answer


Q20) The number of wavelengths, in the visible spectrum is Show Answer


Q21) Which of the following electromagnetic radiations have the smallest wavelength ? Show Answer


Q22) An electromagnetic radiation has an energy 14.4 keV. To which region of electromagnetic spectrum does it belong ? Show Answer


Q23) The area to be covered for T.V. telecast is doubled. Then the height of transmitting antenna ( T.V. tower ) will have to be Show Answer


Q24) The frequency from 3 to 30 MHz is known as Show Answer


Q25) Which of the following represents an infrared wavelength ? Show Answer


Q26) In FM, modulation is doubled. This is possible if frequency deviation is Show Answer


Q27) Radio waves of constant amplitude can be generated with Show Answer


Q28) The process of superimposing signal frequency ( i.e. audio wave ) on the carrier wave is known as Show Answer


Q29) A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the core - cladding interface ? Show Answer


Q30) Broadcasting antennas are generally Show Answer


Q31) The radiowaves of frequency 300 MHz to 3000 MHz belong to Show Answer


Q32) The electromagnetic waves of frequency 2 MHz to 30 MHz are Show Answer


Q33) The maximum range of ground or surface wave propagation depends on Show Answer


Q34) The maximum magnetic field is Show Answer


Q35) The maximum electric force on the electron is Show Answer


Q36) The maximum magnetic force on the electron is Show Answer


Q37) The curve drawn between velocity and frequency of a photon in vacuum will be Show Answer


Q38) Velocity of Electromagnetic Waves in a medium depends upon Show Answer


Q39) Clouds are contained in a layer from the earth’s surface, which is called Show Answer


Q40) Molybdenum is used as a target element for the production of X-rays because it is Show Answer


Q41) A radiation of 200 W is incident on a surface which is 60% reflecting and 40% absorbing. The total force on the surface is Show Answer


Q42) According to Maxwell’s hypothesis, changing electric field gives rise to Show Answer


Q43) Ozone layer blocks the radiations of wavelength Show Answer


Q44) The Electromagnetic theory of light failed to explain Show Answer


Q45) A layer of ionosphere does not reflect waves with frequencies greater than 10 MHz; then maximum electron density in this layer is Show Answer


Q46) X-rays are produced by jumping of Show Answer


Q47) The density of air at the top of mesosphere in comparison to that of near the earth’s surface is Show Answer


Q48) The wavelength of infrared rays is of the order of Show Answer


Q49) The speed of electromagnetic Wave in vacuum depends upon the source radiation. It Show Answer


Q50) 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
Show Answer


Q51) The temperature variation in the region of stratosphere lies from Show Answer


Q52) Radio wave diffract around building although light waves do not. The reason is that radio waves Show Answer


Q53) The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to Show Answer


Q54) 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) Show Answer


Q55) A radar sends the waves towards a distant object and receives the signal reflected by object. These waves are Show Answer


Q56) Which of the following rays is emitted by a human body? Show Answer


Q57) Which of the following relation is correct? Show Answer


Q58) The frequency 1057 MHz of radiation arising from two close energy levels in hydrogen belongs to Show Answer


Q59) X-ray are not used for radar purpose, because they are not Show Answer


Q60) If alpha, beta and gamma rays carry same momentum, which has the longest wavelength? Show Answer


Q61) If the earth did not have atmosphere, its surface temperature on a day time would be Show Answer


Q62) Which is having minimum wavelength? Show Answer


Q63) Which of the following shows green house effect? Show Answer


Q64) 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 Show Answer


Q65) An electromagnetic radiation has an energy of 13.2 keV. Then the radiation belongs to the region of Show Answer


Q66) Out of the following electromagnetic radiation, which has the shortest wavelength? Show Answer


Q67) The fact that radiosignals reach the earth from outside the atmosphere, was discovered accidently by Show Answer


Q68) The ozone layer of the atmosphere lies in the region called Show Answer


Q69) Maxwell in his famous equation of electromagnetism introduced the concept Show Answer


Q70) 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 Show Answer


Q71) Electromagnetic Waves can be deflected by Show Answer


Q72) Electric fields induced by changing magnetic fields are Show Answer


Q73) The correct sequence of the increasing wavelength of the given radiation sources is Show Answer


Q74) Maxwell in his famous equation of electromagnetism introduced the concept of Show Answer


Q75) 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? Show Answer


Q76) The energy of X-ray photon is 2200 eV. Its frequency would be Show Answer


Q77) According to Maxwell’s hypothesis, a changing electric field gives rise to Show Answer


Q78) The shortest wavelength of X-rays emitted from an X-rays tube depends upon Show Answer


Q79) Hydrogen atom does not emit X-rays because Show Answer


Q80) The waves which have revolutionized telecommunication in more recent time, are Show Answer


Q81) 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 Show Answer


Q82) 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 Show Answer


Q83) According to Maxwell’s equation the velocity of light in any medium is expressed as Show Answer


Q84) Height h of transmitter antenna when R is radius of earth to have range d is Show Answer


Q85) The voltage applied across an X-ray tube is nearly equal to Show Answer


Q86) An Electromagnetic Wave has Show Answer


Q87) The waves which are reflected back to the earth by ionosphere is Show Answer


Q88) A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is Show Answer


Q89) In an Electromagnetic Wave, direction of propagation is in the direction of Show Answer


Q90) 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 Show Answer


Q91) The oscillating electric and magnetic field vectors of electromagnetic wave are oriented along Show Answer


Q92) The electric field for a plane electromagnetic wave travelling in the positive z-direction is represented by which one of the following? Show Answer


Q93) Television signals reach us only through the ground waves. The range R related with the transmitter height h is in proportion to Show Answer


Q94) Solar radiation is Show Answer


Q95) 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 Show Answer


Q96) Ground waves have wavelength Show Answer


Q97) The wavelength of X-rays lies between Show Answer


Q98) Which of the following is absorbed by the ozone layer? Show Answer


Q99) The small ozone layer on top of the atmosphere is crucial for human survival because it Show Answer


Q100) The atmosphere above the height of 80 km is called Show Answer


Q101) The atmosphere between the heights of 50 km and 80 km is called Show Answer


Q102) If a free electron is placed in the path of a plane electromagnetic wave, it will start moving along Show Answer


Q103) Infrared radiation is detected by Show Answer


Q104) All components of the Electromagnetic Spectrum in vacuum have the same Show Answer


Q105) 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 Show Answer


Q106) The ozone layer absorbs Show Answer


Q107) Which of the following has zero average value in a plane electromagnetic wave? Show Answer


Q108) Which of the following electromagnetic waves have the longest wavelength? Show Answer


Q109) While tuning in a certain broadcast station with a receiver, we are actually Show Answer


Q110) The principle of laser action involves Show Answer


Q111) The modulation technique used for transforming digital data into analog signals are Show Answer


Q112) A laser device produces amplification in the Show Answer


Q113) Broadcasting antennas are generally Show Answer


Q114) Fading is the variation in the strength of a signal at a receiver due to Show Answer


Q115) Which one of the following is incorrect statement in the transmission of electromagnetic waves? Show Answer


Q116) Because of tilting which waves finally disappear Show Answer


Q117) Faintest stars are called Show Answer


Q118) A geo-synchronous satellite is Show Answer


Q119) If the area to be covered for TV telecast is doubled, then height of transmitting antenna (TV tower) will have to be Show Answer


Q120) A transmitter transmits the message in original Show Answer


Q121) In satellite communication, the communication satellite; Show Answer


Q122) The galaxy in which we live is Show Answer


Q123) In which frequencies range space waves normally propagated Show Answer


Q124) A microphone converts Show Answer


Q125) The modulation in which pulse duration varies in accordance with the modulating signal is called Show Answer


Q126) If a radio receiver amplifies all the signal frequencies equally well, it is said to have high Show Answer


Q127) Modulation is the phenomenon of Show Answer


Q128) The process of superimposing signal frequency (i.e., audio wave) on the carrier wave is known as Show Answer


Q129) The population inversion necessary for laser action used in solid state lasers is Show Answer


Q130) Major parts of a communication system are Show Answer


Q131) Numerical aperture of optical fiber is a measure of Show Answer


Q132) Primary constant of a transmission line are Show Answer


Q133) In frequency modulated wave Show Answer


Q134) Long distance short-wave radio broadcasting uses Show Answer


Q135) An antenna is a device Show Answer


Q136) The space wave propagation is utilized in Show Answer


Q137) Which of the following is correct? Show Answer


Q138) Audio signal cannot be transmitted because Show Answer


Q139) Antenna is Show Answer


Q140) In pulse modulation of analog signals, common pulse system employed are Show Answer


Q141) Which of the following is not the main characteristic of laser beam? Show Answer


Q142) A laser beam is used for carrying out surgery because it Show Answer


Q143) A receiver reconstructs the original message after propagation through the channel. Show Answer


Q144) The frequency of a FM transmitter without signal input is called Show Answer


Q145) Ozone layer above earth's atmosphere will not Show Answer


Q146) A signal emitted by an antenna from a certain point can be received at another point of the surface in the form of Show Answer


Q147) The losses in transmission lines are Show Answer


Q148) Which of the following is the disadvantage of FM over AM Show Answer


Q149) Advantage of optical fibre is Show Answer


Q150) Basically, a communication system is a Show Answer


Q151) When electromagnetic waves enter the ionised layer of ionosphere, then the relative permittivity
ie,dielectric constant dielectric constant of the ionised layer Show Answer


Q152) Laser beams are used to measure long distances because Show Answer


Q153) Basically, the product modulator is Show Answer


Q154) The phenomenon by which light travels in an optical fibres is Show Answer


Q155) The output stage of a television transmitter is most likely to be a Show Answer


Q156) Small vales of numerical aperture (NA) decrease the pulse dispersion but increase losses due to Show Answer


Q157) A modem is a Show Answer


Q158) Optical fibre works on the principle of Show Answer


Q159) Large band width for higher data rate is achieved by using Show Answer


Q160) Venus looks brighter than other stars, due to Show Answer


Q161) The SKIP ZONE in Radio Wave Transmission is that range where Show Answer


Q162) Which is more advantageous? Show Answer


Q163) Which one of the following is a full duplex transmission system? Show Answer


Q164) A laser is a coherent source because it contains Show Answer


Q165) In amplitude modulation, carrier wave frequencies are Show Answer


Q166) The population inversion in helium-neon laser is produced by Show Answer


Q167) The closed structure of co-axial cable prevents inner copper wire or core or from radiating signal power. The statement is Show Answer


Q168) Of the following which is preferred modulation scheme for digital communication Show Answer


Q169) In ruby laser, the stimulated emission is due to transition from Show Answer


Q170) A laser beam is used for locating distant objects because Show Answer


Q171) The principle used in the transmission of signal through an optical fibre is Show Answer


Q172) Which fibers are less expensive and simple to construct? Show Answer


Q173) Intelsat satellite is used for Show Answer


Q174) In the communication systems, AM is used for broadcasting because Show Answer


Q175) The special theory of relativity is based on the frame of reference which has constant? Show Answer


Q176) Through which mode of propagation, the radio waves can be sent from one place to another Show Answer


Q177) Optical fiber communication is generally preferred over general communication system because Show Answer


Q178) In space communication, the sound waves can be sent from one place to another Show Answer


Q179) In frequency modulation Show Answer


Q180) 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 Show Answer


Q181) The main objective of an optical source is Show Answer


Q182) The range of frequencies allotted for FM radio is Show Answer


Q183) The transmission media can be Show Answer


Q184) 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 Show Answer


Q185) Point to point communication requires the use of Show Answer


Q186) What type of modulation is employed in India for radio transmission Show Answer


Q187) The layer of earth's atmosphere responsible for absorbing a large portion of ultraviolet radiations by the sun is Show Answer


Q188) Which of the following device is fully duplex Show Answer


Q189) Special theory of relativity states that Show Answer


Q190) Modulation is the process of superposing Show Answer


Q191) In which of the following remote sensing technique is not used Show Answer


Q192) The electromagnetic waves of frequency 2 MHz to 30 MHz are used Show Answer


Q193) The frequency band used in the downlink of satellite communication is Show Answer


Q194) The attenuation in optical fibre is mainly due to Show Answer


Q195) Present day communication systems are Show Answer


Q196) Flash spectrum confirms a/an Show Answer


Q197) Which of the following four alternatives is not correct? We need modulation Show Answer


Q198) For maximum power transfer to the load, impedance of the detecting device must be equal to characteristic impedance of the transmission line Show Answer


Q199) Quality of transmission depends only Show Answer


Q200) In a communication system, noise is most likely to affect the signal Show Answer


Q201) In co-axial cable the material used as spacer is Show Answer


Q202) The modulation technique used for transforming digital data into analog signals are Show Answer


Q203) The principle of laser action involves Show Answer


Q204) While tuning in a certain broadcast station with a receiver, we are actually Show Answer


Q205) What is the range of the characteristic impedance of a coaxial cable? Show Answer


Q206) The velocity of electromagnetic waves in a dielectric medium of constant 4 is Show Answer


Q207) Identify the incorrect statement from the following Show Answer


Q208) The velocity of a particle at which the kinetic energy is equal to its rest energy is Show Answer


Q209) The difference in the refractive index of the fiber core and fiber cladding in step-index fibers is typically Show Answer


Q210) In amplitude modulation, the bandwidth is Show Answer


Q211) Consider telecommunication through optical fibres. Which of the following statements is no true? Show Answer


Q212) Which of the following explain that all galaxies are receding from us? Show Answer


Q213) 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 Show Answer


Q214) 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? Show Answer


Q215) The modulation index of a FM signal is 0.25. If modulating frequency is 2kHz, the maximum derivative in frequency would be Show Answer


Q216) The resistance of copper wire of diameter=2 mm is of the order of Show Answer


Q217) A 1000kHz carrier wave is modulated by audio signal of frequency range 100-5000Hz. Then the width of the channel in kHz is Show Answer


Q218) Frequency range for microwaves is Show Answer


Q219) 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 Show Answer


Q220) The waves relevant to telecommunications are Show Answer


Q221) 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 Show Answer


Q222) The length of a half wave dipole at 30 MHz is Show Answer


Q223) In space communication, the information can be passed from one place to another at a distance of 100 km in Show Answer


Q224) 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 Show Answer


Q225) A carrier is simultaneously modulated by two sine waves having modulation indices of 0.3 and 0.4. The total modulation index will be Show Answer


Q226) 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 Show Answer


Q227) What is the minimum length of antenna required to transmit a radio signal of frequency 20 MHz? Show Answer


Q228) 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 Show Answer


Q229) Which of the following statements is wrong? Show Answer


Q230) For a body moving with relativistic speed, if the velocity is doubled, then Show Answer


Q231) In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be Show Answer


Q232) Range of frequencies allotted for commercial UHF TV broadcast is Show Answer


Q233) What fraction of the surface area of earth can be covered to establish communication by one geostationary satellite? Show Answer


Q234) 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 Show Answer


Q235) When radio waves passes through ionosphere, phase difference between space current and capacitive displacement current is Show Answer


Q236) 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 Show Answer


Q237) 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
Show Answer


Q238) 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 Show Answer


Q239) 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. Show Answer


Q240) The diameter of an optical fiber is Show Answer


Q241) The characteristic impedance of a coaxial cable is of the order of Show Answer


Q242) The cladding material of optical fibre has refractive index Show Answer


Q243) 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 Show Answer


Q244) According o Hubble’s law the red-shift (Z) of a receding galaxy and its distance r from earth are related as Show Answer


Q245) Which of the following frequencies will be suitable for beyond the horizon communication Show Answer


Q246) An antenna is of height 500 m. What will be its range (Radius of earth is 6400 km)? Show Answer


Q247) The antenna current of an AM broadcast transmitter modulated by 50% is 11. Find the carrier current Show Answer


Q248) 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 Show Answer


Q249) 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 Show Answer


Q250) The velocity of electromagnetic wave in good conductor is Show Answer


Q251) The bit rate for a signal, which has a sampling rate of 8 kHz and where 16 quantisation levels have been used is Show Answer


Q252) 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 Show Answer


Q253) Ozone layer blocks the radiations of wavelength Show Answer


Q254) Which one of the following statements is wrong? Show Answer


Q255) A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the corecladding interface Show Answer


Q256) If sky wave with frequency of 50 MHz is incident on D region at an angle of 30°, then angle of refraction is Show Answer


Q257) When the modulation percentage is 75, an AM transmitter produces 10 kW. How much of this is carrier power? Show Answer


Q258) To cover a population of 20 lakh, a transmission tower should have a height … (Radius of earth = 6400 km, population per square km =1000) Show Answer


Q259) 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) Show Answer


Q260) The fundamental radio antenna is a metal rod which has a length equal to Show Answer


Q261) Let A = light obtained by stimulated emission and B = light obtained by spontaneous, then Show Answer


Q262) 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 Show Answer


Q263) In earth's atmosphere, for F1-layer; the virtual height and critical frequency are Show Answer


Q264) 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 Show Answer


Q265) 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 Show Answer


Q266) An oscillator is producing FM waves of frequency 2 kHz with a variation of 10 kHz. What is the modulating index? Show Answer


Q267) A transmitter supplies 9 kW to the aerial when unmodulated. The power radiated when modulated to 40% is Show Answer


Q268) 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 Show Answer


Q269) The velocity factor of a transmission line is x. If dielectric constant of the medium is 2.6, the value of x is Show Answer


Q270) 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 Show Answer


Q271) 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) Show Answer


Q272) 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 Show Answer


Q273) 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 Show Answer


Q274) Electromagnetic waves with frequencies greater than the critical frequency of ionosphere cannot be used for communication using sky wave propagation, because Show Answer


Q275) For good demodulation of AM signal of carrier frequency f, the value of RC should be Show Answer


Q276) 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 Show Answer


Q277) The sky wave propagation is suitable for radio-waves of frequency Show Answer


Q278) For sky wave propagation of 10 MHz signal, what should be the minimum electron density in ionosphere? Show Answer


Q279) 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 Show Answer


Q280) 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 Show Answer


Q281) Which frequency range is used for optical communication? Show Answer


Q282) A TV tower has a height of 75 m. What is the maximum area upto which this TV communication can be possible? Show Answer


Q283) If both the length of an antenna and the wavelength of the signal to be transmitted are doubled, the power radiated by the antenna Show Answer


Q284) An AM wave has 1800 watt of total power content. For 100% modulation the carrier should have power content equal to Show Answer


Q285) What is the modulation index of an over modulated wave Show Answer


Q286) In AM, the centpercent modulation is achieved when Show Answer


Q287) What should be the velocity of an object so that it’s mass becomes twice of its rest mass? Show Answer


Q288) An antenna behaves as resonant circuit only when its length is Show Answer


Q289) 1000 kHz carrier wave is amplitude modulated by the signal frequency 200-4000 Hz. The channel width of this case is Show Answer


Q290) The range of characteristics impedance for co-axial wire lines is Show Answer


Q291) If the maximum amplitude of an amplitude modulated wave is 25 V and the minimum amplitude is 5 V, the modulation index is Show Answer


Q292) What happens inside optical fibre? Show Answer


Q293) 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 Show Answer


Q294) The velocity factor of a transmission line is related to dielectric constant K of the medium is Show Answer


Q295) Day time ionosphere comprises of Show Answer


Q296) The transmission of high frequencies in a coaxial cable is determined by Show Answer


Q297) The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to Show Answer