EXERCISE 12A 



WHAT ARE THE DIFFERENT AREAS COVERED BY A BEAM OF LIGHT STRIKING THE 

 SURFACE OF THE EARTH AT DIFFERENT ANGLES? 



Materials. The representation of angles shown on this sheet. 



Directions. Let the horizontal line in the figure below represent the surface of the earth. Line a 

 is drawn so that it makes an angle of 72.5 as labeled, and line b makes an angle of 25.5. These are 

 approximately the angles which the sun's beams make in summer and winter, respectively, at a lati- 

 tude of 41. Draw a line parallel to line a at a distance of 2 centimeters from it. The length of the 

 base line between the two intersections will then represent the length of a rectangular area covered by a 

 beam of light 2 centimeters square. Taking this line as the length of the rectangle, complete the 

 rectangle below the line, making it 2 centimeters wide. Calculate from its dimensions the number of 

 square centimeters covered by a beam of light 2 centimeters square striking the earth's surface at an 

 angle of 72.5. 



Draw a line parallel to line b and 2 centimeters from it ; let the length of the base line between 

 the two intersections represent the length of the area covered by a beam of light striking the earth 

 at an angle of 25.5. Using the width of the beam as 2 centimeters, complete the rectangle and 

 calculate the area. 



What do you conclude from the above work ? How many times larger than the first area is the 

 area covered by the beam striking the earth at an angle of 25.5 ? Why is it warmer in summer 

 than in winter? 



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[17] 



