英语六级听力练习之隧道与广播
<p> 隧道与广播</p><p> <span word="How">How</span> <span word="come">come</span> <span word="we">we</span> <span word="can">can</span> <span word="hear">hear</span> <span word="FM">FM</span> <span word="longer">longer</span> <span word="in">in</span> <span word="a">a</span> <span word="tunnel">tunnel</span> <span word="than">than</span> <span word="AM">AM</span>?</p><p> 为什么在隧道中调频广播比调幅广播的信号要好一点?</p><p> <span word="Its">Its</span> <span word="because">because</span> <span word="FM">FM</span> <span word="stations">stations</span> <span word="transmit">transmit</span> <span word="at">at</span> <span word="higher">higher</span> <span word="frequencies">frequencies</span>. <span word="They">They</span> <span word="generally">generally</span> <span word="go">go</span> <span word="from">from</span> <span word="eighty">eighty</span>-<span word="eight">eight</span> <span word="to">to</span> <span word="one">one</span>-<span word="hundred">hundred</span>-<span word="and">and</span>-<span word="eight">eight</span> <span word="megahertz">megahertz</span>. <span word="Thats">Thats</span> <span word="over">over</span> <span word="a">a</span> <span word="hundred">hundred</span> <span word="million">million</span> <span word="cycles">cycles</span> <span word="per">per</span> <span word="second">second</span>.</p><p> 这是因为调频广播台的传播频率要频繁些。通常在88到108兆赫。即每秒转1亿圈。</p><p> <span word="As">As</span> <span word="a">a</span> <span word="result">result</span>, <span word="a">a</span> <span word="single">single</span> <span word="radio">radio</span> <span word="wave">wave</span> <span word="from">from</span> <span word="an">an</span> <span word="FM">FM</span> <span word="station">station</span> <span word="is">is</span> <span word="only">only</span> <span word="a">a</span> <span word="few">few</span> <span word="meters">meters</span> <span word="long">long</span>, <span word="about">about</span> <span word="the">the</span> <span word="size">size</span> <span word="of">of</span> <span word="a">a</span> <span word="car">car</span>. <span word="An">An</span> <span word="AM">AM</span> <span word="station">station</span> <span word="is">is</span> <span word="putting">putting</span> <span word="out">out</span> <span word="radio">radio</span> <span word="waves">waves</span> <span word="that">that</span> <span word="are">are</span> <span word="hundreds">hundreds</span> <span word="of">of</span> <span word="times">times</span> <span word="as">as</span> <span word="long">long</span>!</p><p> 因此，调频广播电台发出的一个电波的长度只有几米，大概是一辆车的大小。而调幅广播站发出的电波长达几百米。</p><p> <span word="Long">Long</span> <span word="wavelengths">wavelengths</span> <span word="tend">tend</span> <span word="to">to</span> <span word="be">be</span> <span word="absorbed">absorbed</span> <span word="or">or</span> <span word="blocked">blocked</span> <span word="as">as</span> <span word="they">they</span> <span word="try">try</span> <span word="to">to</span> <span word="enter">enter</span> <span word="the">the</span> <span word="smaller">smaller</span> <span word="tunnel">tunnel</span>. <span word="The">The</span> <span word="higher">higher</span>-<span word="energy">energy</span> <span word="and">and</span> <span word="shorter">shorter</span>-<span word="wavelength">wavelength</span> <span word="waves">waves</span> <span word="from">from</span> <span word="an">an</span> <span word="FM">FM</span> <span word="station">station</span> <span word="arent">arent</span> <span word="absorbed">absorbed</span> <span word="or">or</span> <span word="blocked">blocked</span> <span word="as">as</span> <span word="much">much</span>. <span word="Instead">Instead</span>, <span word="they">they</span> <span word="tend">tend</span> <span word="to">to</span> <span word="bounce">bounce</span> <span word="around">around</span> <span word="and">and</span> <span word="get">get</span> <span word="reflected">reflected</span> <span word="off">off</span> <span word="of">of</span> <span word="surfaces">surfaces</span>, <span word="much">much</span> <span word="like">like</span> <span word="the">the</span> <span word="inside">inside</span> <span word="of">of</span> <span word="a">a</span> <span word="tunnel">tunnel</span>.</p><p> 在穿越隧道时，长的波长会被吞并阻碍。而来自调频广播高能量，波长又短的电波则不会被吞并或阻碍。相反的，它们会被隧道表面反射回来。</p><p> <span word="Of">Of</span> <span word="course">course</span>, <span word="they">they</span> <span word="only">only</span> <span word="bounce">bounce</span> <span word="so">so</span> <span word="far">far</span>. <span word="If">If</span> <span word="the">the</span> <span word="tunnel">tunnel</span> <span word="is">is</span> <span word="long">long</span> <span word="enough">enough</span>, <span word="even">even</span> <span word="FM">FM</span> <span word="stations">stations</span> <span word="fade">fade</span> <span word="out">out</span> <span word="until">until</span> <span word="you">you</span> <span word="come">come</span> <span word="out">out</span> <span word="the">the</span> <span word="other">other</span> <span word="end">end</span>.</p>
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