Dạng bài Đọc hiểu lớp 12
Why was Townes’ early work with stimulated emission done with microwaves?
Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions.
The word laser was coined as an acronym for Light Amplification by the Stimulated Emission of Radiation. Ordinary light, from the Sun or a light bulb, is emitted spontaneously, when atoms or molecules get rid of excess energy by themselves, without any outside intervention. Stimulated emission is different because it occurs when an atom or molecule holding onto excess energy has been stimulated to emit it as light.
Albert Einstein was the first to suggest thc existence of stimulated emission in a paper published in 1917. However, for many years physicists thought that atoms and molecules always were much more likely to emit light spontancously and that stimulated emission thus always would be much weaker. It was not until after the Second World War that physicists began trying to make stimulated emission dominate. They sought ways by which, one atom or molecule could stimulate many others to emit light, amplifying it to much higher powers.
The first to succeed was Charles H. Townes, then at Columbia University in New York. Instead of working with light, however, he worked with microwaves, which have a much longer wavelength, and built a device he called a “maser”, for Microwave Amplification by the Stimulated Emission of Radiation. Although he thought of the key idea in 1951, the first maser was not compleled until a couple of years later. Before long, many other physicists were building masers and trying to discover how to produce stimulated emission at even shorter wavelengths.
The key concepts emerged about 1957. Townes and Arthur Schawlow, then at Bell Telephone Laboratories, wrote a long paper outlining the conditions needed to amplify stimulated emission of visible light waves. At about the same time, similar ideas crystallized in the mind of Gordon Gould, then a 37-year-old graduate student at Columbia, who wrote them down in a series of notebooks. Townes and Schawlovs published their ideas in a scientific journal, Physical Review Letters, but Gould files a patent application. Three decades later, people still argue about who deserves the credit for the concept of the laser.
Câu 13401: Why was Townes’ early work with stimulated emission done with microwaves?
A. He was not concerned with light amplification.
B. It was easier to work with longer wavelengths.
C. Schawlow had already begun work on the laser.
D. The laser had already been developed.
Quảng cáo
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Đáp án : B(0) bình luận (0) lời giải
Giải chi tiết:
Why was Townes’ early work with stimulated emission done with microwaves? (Tại sao công trình ban đầu của Townes về bức xạ kích thích được tiến hành với sóng điện từ?)
Đáp án đúng là B: "It was easier to work with longer wavelengths ” (Nghiên cứu sóng cỏ bước sóng dài thì dễ dàng hơn).
Ý trong bài: “Instead of working with light, however, he worked with microwaves, which have a much longer wavelength... Before long, many other physicists were... trying to discover how to produce stimulated emission at even shorter wavelengths” (Tuy nhiên thay vì nghiên cứu ánh sáng, ông ta nghiên cứu sóng điện từ có bước sóng dài hơn nhiều... Trước đó khá lâu các nhà vật lí cổ khám phá ra cách kích thích bức xạ phát ra với sóng điện từ có bước sóng ngắn hơn) (nhưng họ đã thất bại).
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