题目

Can storms in Africa cause asthma(哮喘) in the Caribbean(加勒比)? Islanders point to the desert insects that land on beaches after a 5,000-kilometer flight across the Atlantic. If they can use winds to get from one continent to another, so can clouds of dust that carry disease.Scientists think that as Africa becomes drier, dust from expanding deserts is being blown away into Caribbean islands. A study in Barbados shows that asthma has increased 17 times since Africa’s drought(干旱) began in 1973.Other forms of life are suffering, too. Among them are the Caribbean’s famous coral reef一列电磁波在通过玻璃时，共用10﹣10s，在这段过程中总共振荡20次，如果它振荡一次传播的距离是1mm．求：（1）此玻璃的厚度是多少？（2）这列电磁波如果要通过7.6cm厚的玻璃所用的时间是多少？