Microwavesthattransmittelevisionsignalsalwaystravelinastraightline.Becausetheearthisrounditisimpossibletosendtelevisionsignalsoveralongdistance.Forexampleifwetriedtosendtelevisionsignalsdirectlyf
Microwavesthattransmittelevisionsignalsalwaystravelinastraightline.Becausetheearthisrounditisimpossibletosendtelevisionsignalsoveralongdistance.Forexampleifwetriedto sendtelevisionsignalsdirectlyfromEuropetoAmericathemicrowavescarryingthesignalswouldshootintospaceovertheAtlanticandwouldreachAmerica.
Ifwewanttosendtelevisionsignalsaroundthesurfaceoftheearthwemustsendthemfrompointtopointbytherelaysystem.Onlandwecansetuprelaystationsforthispurposeandwecanpasssignalsfromstationtostationinaseriesofstraightlines.Howeverwecannotdothissoeasilyoverwater.InordertosendpicturesdirectlyacrosstheAtlanticforexamplewewouldneedtobuildachainofrelaystationsacrosstheoceanwhichisabout3000mileswide.Onechoicewouldbetobuildonegreattowerinthemiddleoftheocean.Butthetowerwouldhavetobe500mileshigh!
Bothoftheideasareimpossible.SoweusethecommunicationsatellitethousandsofmilesinouterspacetorelaythetelevisionsignalsacrosstheAtlantic.AsatellitereceivesthepicturesignalsinastraightlinefromthegroundstationononesideoftheAtlanticfromEnglandforexample.ThenitsendssignalsdownagainalsoinastraightlinetothegroundstationontheothersideoftheAtlanticintheUnitedStates.Thecommunicationsatellitemustbewithinviewofbothgroundstationsatthesametime.
1.Whataremicrowaves?
A.Theyarelightwavesthatareuseless.
B.Theyareradiationwhichcantravelstraight.
C.Theyarenotwaves.
D.TheyareveryshortwavesusedinTVandradar.
2.Whyshouldpeoplebuildrelaystations?
A.Becausethemicrowavescannottravelalongtime.
B.Becausethemicrowavesarestrongenoughtoreachanotherplace.
C.Becausethemicrowavestravelinastraightlineandtheearthisround.
D.Becausepeoplewanttoshowtheirpower.
3.Televisionsignalsmustbesent________.
A.fromcitytocity
B.frompointtopoint
C.fromhousetohouse
D.frombuildingtobuilding
4.What’sthemainreasonforustousesatellitestorelayTVprogrammes?
A.Satellitescancoverlargeareas.