EXERCISE 16:Read 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.
Question 97: What is the best title for the passage?
- The history of the photoflash
- Theories about how the eye reacts to light
- The technology of modern photography
- The dangers of using the early photoflash
Question 98: According to the passage, an advantage of using a photoflash is that it .
A. can produce repeated bursts of light B. intensities colors in photographs
C. is short enough not to bother human eyes D. supplements existing lighting
Question 99: The word "ignited" in paragraph 1 is closest in meaning to .
A. set on fire B. cut into C. opened D. shaken
Question 100: Which of the following is TRUE about the function of the glass in the first flashbulbs?
- It produced the spark that initiated the flash.
- It magnified the light produced by the flash.
- It protected the photographer from the heat of the flash.
- It kept the metal and oxygen apart before the flash.
Question 101: The word "it" in paragraph 2 refers to .
A. oxygen B. battery C. wire D. current
Question 102: The word "momentarily" in paragraph 2 is closet in meaning to .
A. effortlessly B. briefly C. electronically D. gradually
Question 103: According to the passage, what helps a flashbulb burn longer?
A. thicker wire B. more oxygen
C. thinner glass D. continuous electricity
Question 104: Which of the following most accurately reflects the main idea of the last paragraph?
- The time when photoflash was first used.
- How metal burns in an atmosphere of pure oxygen.
- How early photoflash worked.
- The role of glass in flashbulb.
