题目内容
The basic principle of radar is illustrated by what happens when one shouts in a e. The echoof the shouting 11 the walls helps a person determine the size of i cave. With radar, however , the waves are radio waves instead of 12 waves. dio waves travel 13 the speed of light, about 300,000 kilometers in a second. A lar set 14 a short burst of radio waves. Then it receives the echoes 15 when waves bounce (Silt) off objects. By determining the time it 16 for the echoes to imi to the radar set, a trained technician 17 determine the distance between the [ar set and other objects. The word "radar", 18 , gets its name from the term dio detection and ranging." "Ranging" is the term for detection of the 19 between object and the radar set.
Besides being of critical importance to pilot, radar is 20 for air traffic control, tracking ships at sea, and for tracking weather systems and storms.
11.
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