34.(1)0.8(3分)负(2分)解析:若波沿x轴正方向传播,传播时间△t=(n+)T(n=0,1,2…),周期T=4n+1当n=0时,T最大,最大值为T灬=4t=0.8s.若波的传播速度为55m/s,波在△t=0.2s时间内传播的距离为△x=△=11m=2x+3根据波形的平移法得到,波的传播方向是沿x轴负方向2)根据全反射条件得全反射临界角C=45°(1分)光线射入三棱镜后,在AC边的入射角为30°,不会发生全反射.(1分设射出AC边时的出射角为i,根据折射定律有sin30°=n,解得i=45°(1分)根据题意,如图所示,射到光屏上最低点的位置在图中S1点.由几何关系可知,∠OCS1=30故OS1=3Ltan30°=3L(2分)光线在BC边的入射角为75°,大于全反射临界角45°,会发生全反射(1分)由题意可知,从BC边全反射的光线中射到光屏上最高点的位置在图中S2点,如图所示,由几何关系可知,∠OBS2=15°故OS2=4Ltan15°=(8-4√3)L(2分)所以,光屏上光斑的最高点和最低点之间的距离为s=0s1+OS2=(8-3√3)L(2分)

书面达I'm delighted to know that you are going to ukpart in. Chinese poetry recitation contest. The factthat you are so interested in Chinese culture makes mhappy Now I'd like to offer you some practical adviceFirstly, you should have a better understanding ofwhat you are going to read. Only by doing this can youappreciate its beauty. Secondly, correct your pronuneation by listening to Chinese radio programs because allannouncers speak standard Chinese. What'sgood idea to make some Chinese friends and cote with then as often as possible, which can improve your spoken ChiI hope my opare of help to you and wishyou good luck andYours.Li H

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