2 Progress Test U9 U10 - Page2

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READING

5 points


Read the text. The sentences in the boxes were removed from the text. Can you decide which sentence goes where?


A. The intensity of the light which can be produced in this way depends on the size and power of the flash unit.


B. He was a professor at the Massachusetts Institute of Technology.


C. There are also large flash units used in studios that can be plugged into an electric wall socket.


When it is too dark to take a picture with a camera in natural light, photographers need to have an additional source of light. The device which is used to produce artificial light for this purpose is called an electronic flash unit, commonly called a flash. The electronic flash unit was invented by an American engineer Harold Eugene Edgerton. 1.............................................................................................................................................. .

A

B

C


Some flash units are small and built into cameras. Some are battery-powered and can be mounted on the camera when needed. 2.............................................................................................................................................. .

A

B

C


An electronic flash unit consists of a glass quartz tube which is filled with gas (most usually, xenon), with electrodes at both ends. When electricity reaches the tube, the gas produces an intense burst of light that lasts for a very short time, for example, for 1/1000 or 1/5000 of a second. 3..........................................................................................................................................

A

B

C



Decide if these sentences are true or false.


All flash units are battery-powered.

True

False


Electricity is necessary for a flash unit to work.

True

False



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