1、　 透镜

(1)观察课本P2的图6-1，图中列出的6种透镜在结构上有什么不同？按结构分成两类，一类是　　　　 ，特点是　　　　　　　 　　　　　　　　　　　　　　　　

另一类是　　　　　 ，特点是　　　　　　　　　　　　　　　　　　　　　　 　

(2)透镜的相关名词：

①主轴：　　　　　　　　　 叫主轴，在课本图6-2中，C1C2即是透镜的主轴。

②光心：　　　　　　　　　 叫光心，在课本图6-2中，O点即是透镜的 光心。

经过光心的光线的传播方向　　　　 　。

(3)画图练习：在下面画出并标出凸透镜和凹透镜的主轴和光心。

3、　 做一做：

2、　 光的折射规律是什么？

1、　 什么是光的折射？

55. The aim of the passage is to ______.

　　 A. praise Ian Findlay for his work　　　

　　 B. report a piece of interesting news

　　 C. inform us of the wide use of DNA testing　

54. The last paragraph suggests that ______.

A. the immediate adopting of the technology may cause mistakes

B. the public have acknowledged the new testing technology

C. it is safe to put the new technology into use now

D. Dr Findlay is quite sure of his new technology

53. According to Ian Findlay, the new technology can ______.

A. help to keep DNA evidence fresh for decades and even centuries

B. make the process of DNA testing much more simplified

C. help to pick up DNA identities more easily

D. be widely used in five years at most

52. The underlined word" validated" means ______.

　　　 A. confirmed　 　　　 B. imagined　 　　　　　 C. supposed　 　　　　 D. criticized

51. The main advantage of the new technology is that ______.

A．a single cell can identify an individual

　 B．it has brought down the cost of DNA testing

　　　 C．a higher level of accuracy can be acquired with a single cell

　　　 D．it needs less than 200 cells to gain a certain level of accuracy

50. In this passage, the writer mainly　　　 .

A. describes two types of people　　　　

B. laughs at the unhappy people

C. suggests ways to help the unhappy　　

D. tells people how to be happy in life

C

An Australian-based scientist announced yesterday he had made a step forward in forensic (用于法庭的) DNA testing so that an individual can be identified by a single cell.　　　

Ian Findlay, from the Australian Genome Research Facility at the University of Queensland, said current DNA testing required 200 to 500 cells to gain a similar level of accuracy. "What we have done has brought that down to one cell," Dr Findlay said after releasing details of his DNA testing technique at a Sydney conference.　　

The technology could allow investigators to pick up DNA identities from plastic cards and even build up a complete history of the people who have handled a paper document.

"You'd have to wear a space suit to stop yourself from leaving traces. You can identify cells on the paper, so you can work out where it's come from and who's touched it,” he said.

The technique could also be used to trace the thrower of a punch(打孔)from cells left behind on the skin of their victim. Even the wearing of latex(橡胶)gloves would not help: small cells can pass through the gloves, and the constant flow of genetic material given off by the human body would leave further evidence.

"We gained a skin cell from a document dating back 30 years and managed to gain a DNA fingerprint. DNA evidence can remain fresh for decades, perhaps even centuries," Dr Findlay said.　 "The potential for this technology to solve unsolved crimes is great, "he said.　　

But Dr Findlay, named scientist of the year in 1998 by the European Society of Human Genetics, said the new testing needed to be scientifically validated, which would take up to five years.　　　

He said, "There are serious consequences taking on technologies too early. The public has to be sure that they have the utmost confidence in the security and court systems."