【单选题】Without proper planning, tourism can cause problems. For ex ample, too many tourists can crowd public places that are also enjoyed by the inhabitants of a country. If tourists create too much traffic,...
【简答题】.A 、 B 两点有两个相干波源,初相差 ,振幅都为 4cm ,频率 70Hz ,波速 400m/s , AB 距离为 40m , P 为 AB 之间连线上一点,AP:BP=1:3 , 则 A 、 B 波源到达 P 点引起的两个分振动的关系为_______(填‘同相’或‘反相’) , P 点振幅为 _______cm 。