Câu hỏi:
11/04/2020 1,622Read the passage and mark the letter A, B, C or D to answer the following questions.
Most sources of illumination generate light over an appreciable period, and indeed if an object is lit for a very brief time (1ess that 1/25 second), the human eye will not react in time to see the object. A photographic emulsion - that is, a light-sensitive coating on photographic film, paper, or glass - will, however, record much shorter bursts of light. A photographic flash can therefore be used to capture high-speed movement on film as well as to correct deficiencies of the normal surrounding lighting. Photoflash is now generated electronically, but the earliest form, first used in 1864, was a paper bag containing
magnesium wire and some oxygen-rich substance, such as potassium chlorate. When the bag was ignited, the metal burned with an intense flash. A contemporary observer reported that "this quite unsafe device seems to have done nothing worse that engulf the room in dense smoke and lead to pictures of dubious quality and odd poses.”
The evolution of the photoflash was slow, flashbulbs, containing fine wire made of a metal, such as magnesium or aluminum, capable of being ignited in an atmosphere of pure oxygen at low pressure, were introduced only in the 1920's. In the earliest type, the metal was separated from the oxygen by a thin glass bulb. The flash was fired by piercing the bulb and allowing the oxygen to come into contact with the metal, which ignited spontaneously. Later bulbs were fired by an electric battery, which heated the wire by passing a small current through it. Other combinations, such as the pairing of oxygen difluoride with zirconium, have also been used. In each case enough energy is given out to heat the oxidizable metal momentarily to a white hot emission of visible light. The smoke particles are so small that they cool rapidly; but since they are white, they contribute to the brilliance by reflecting the light from their still glowing neighbors. A slightly bigger form of the metal will burn for a longer time.
Which of the following is TRUE about the function of the glass in the first flashbulbs?
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Trả lời:
Giải bởi Vietjack
Đáp án D
Điều nào dưới đây là ĐÚNG về chức năng thủy tinh trong chiếc bóng đèn flash đầu tiên được sử dụng?
A. Nó tạo ra tia lửa để khởi động đèn flash
B. Nó phóng đại ánh sáng do đèn flash tạo ra
C. Nó bảo vệ các nhiếp ảnh gia khỏi sức nóng của đèn flash
D. Nó giữ cho kim loại và oxy tách rời nhau trước khi đèn nháy
Dựa vào thông tin trong đoạn 2:
"In the earliest type, the metal was separated from the oxygen by a thin glass bulb” (Ở loại bóng đèn lần đầu được sử dụng, kim loại được tách rời khỏi oxy bằng một bóng đèn thủy tinh mỏng.)
Nhà sách VIETJACK:
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