问题 计算题

(9分)有一顶角为直角的玻璃砖,放在空气中,一光束斜射入玻璃砖的一个侧面,如图所示,然后投射到它的另一个侧面。若该玻璃砖全反射临界角为42°,问:

①这束光线能否从另一侧面射出?

②若光线能从侧面射出,玻璃砖折射率应满足何条件?

答案

①不能射出    ② n<

题目分析:(2)①由于玻璃的临界角C=42°,所以不论入射角θ1为多少,总有折射角θ2<42°,(1分)

则折射光在另一侧面的入射角θ′1>(90°-42°)=48°>C,(2分)

所以光线在另一侧面发生全反射、不能射出。(1分)

②因θ2总小于临界角,要在另一侧面能射出,θ′1也应小于临界角。

即θ2 < C,(1分)θ′1=(90°-θ2)<C, 解得C >45°.(2分)

这就要求玻璃折射率n满足=sinC>sin45°=, 故解出n<。(2分)

阅读理解

Businesses are witnessing a difficult time, which has in turn produced influence on consumers’ desire to go green. However, shoppers are still laying stress on environmental concerns.

Two thirds of customers say that environmental considerations inform their purchases to the same degree as they did a year ago, while more than a quarter say that they are now even better aware of the environmental effect on what they buy.

This may help to influence how shops store goods on their shelves. And the companies should still make efforts to become more environmentally friendly. Two out of three people think it is important to buy from environmentally responsible companies, with about one in seven saying that they had even decided to take their custom elsewhere if they felt a company’s environmental reputation was not good enough.

Harry Morrison, chief executive(主管)of the Carbon Trust, sympathizes:“I understand this situation where survival is very important now. But from environmental considerations, the clock is ticking—we don’t have much time. In addition, cutting carbon has an immediate effect as costs drop and a medium-term benefit for the brand.”

Larger companies have an extra motivation to look at reducing their carbon footprint, as new rules next year will require businesses to buy carbon allowances to make up for their emissions(排放). Those that have taken early action will have a head start. More than two thirds of consumers are not clear about which companies are environmentally responsible. This suggests that firms that are able to relay clearly their message to the public will be in a pole position to attract shoppers.

The Carbon Trust believes that it can help by informing customers about the good work companies are doing. “When companies are granted(授予)the standard, they can use a logo(标识)in all their marketing which makes it clear that they are working towards cutting emissions,” Mr. Morrison said.

小题1: What’s the main idea of the passage?

A.Businesses are finding ways to send their message to the shoppers.

B.Companies will soon get information about cutting carbon emissions.

C.Firms are making efforts to encourage customers to keep goods at home.

D.Firms are urged to cut carbon emissions by shoppers’ environmental awareness.小题2: The underlined word “inform” in Paragraph 2 probably means“      ”.

A.affect

B.change

C.disturb

D.reject小题3:According to Harry Morrison, businesses          .

A.will benefit from cutting carbon emissions

B.should buy carbon allowances for shoppers

C.are required to make up for their carbon emissions

D.have encouraged shoppers to take their custom elsewhere小题4:We can learn from the passage that businesses will        .

A.have a strong desire to reduce costs

B.use the same logo in their marketing

C.gain advantages by taking early action

D.attract more shoppers by storing goods

单项选择题