搜题请搜索小程序“爱下问搜题”
问题 问答题

如图所示，一列平面波朝着两种介质的界面传播，A1A2是它在介质Ⅰ中的一个波面，A1C1和A2C2是它的两条波线，其入射角为53°，（sin53°=0.8）．C1和C2位于两种介质的界面上．B1B2是这列平面波进入介质Ⅱ后的一个波面．已知A1A2的长度为0.6m，介质Ⅰ和介质Ⅱ中的波速之比为3：4，问：A1C1B1和A2C2B2的长度相差多少？

答案

如图，画出波面C1D1、C2D2，

由

sinθ1
sinθ2
=
v1
v2
得：sinθ2=
v2
v1
sinθ1=
3
4
×0.8=0.6

即θ2=37°，由几何关系可知，∠C2C1D1=θ1，∠C1C2D2=θ2

所以C1C2=1.0m，D1C2=0.8m，C1D2=0.6m

故A1C1B1与A2C2B2的长度相差△r为△r=C2D1-C1D2=0.2m

答：A1C1B1和A2C2B2的长度相差0.2m．

选择题

东南亚居民以单衣薄裙为主。我们这里冬季穿棉夏季穿单。这种衣着习惯主要是受[ ]

A．经济条件的影响

B．物产差异的影响

C．地形的影响

D．气候的影响
查看答案
单项选择题

Attempts to understand the relationship between social behavior and health have their origin in history. Dubos (1969) suggested that primitive humans were closer to the animals (1) they, too, relied’upon their instincts to stay healthy. Yet some primitive humans (2) a cause and effect relationship between doing certain things and alleviating (3) of a disease or (4) the condition of a wound. (5) there was so much that primitive humans did not (6) the functioning of the body, magic became an integral component ofthe beliefs about the causes and cures of heath (7) Therefore it is not (8) that early humans thought that illness was caused (9) evil spirit. Primitive medicines made from vegetables or animals were invariably used in combination with some form of ritual to (10) harmful spirit from a diseased body.

One of the. earliest (11) in the Western world to formulate principles of health care based upon rational thought and (12) of supernatural phenomena is found in the work of the Greek physician Hippocrates. The writing (13) to him has provided a number of principles underiying modern medical practice. One of his most famous (14) , the Hippocratic Oath, is the foundation of contemporary medical ethics.

Hippocrates also argued that medical knowledge should be derived from a (15) of the natural science and the logic of cause and effect relationships. In this (16) thesis, On Air, Water, and Places, Hippocrates pointed out that human well-being is (17) by the totality of environmental (18) : living habits or lifestyle, climate, geography of the land, and the quality of air, and food. (19) enough, concerns about our health and the quality of air, water, and places are (20) very much written in twentieth century.

6（）

A.confirm

B.appreciate

C.tolerate

D.discover
查看答案