EXERCISE 12 



TO DETERMINE THE DIFFERENT AREAS COVERED BY A BEAM OF LIGHT STRIKING 

 THE SURFACE OF THE EARTH AT DIFFERENT ANGLES. 



Materials. Some small blocks of wood 6 or 8 inches long and 1 inch square ; a saw ; a protractor. 



Directions. Suppose that at one time of the year the sun's rays fall at an angle of 72.5, and 

 25.5 at another time of the year. Cut one end of a block of wood at an angle of 72.5 and the 

 other end of the block of wood at an angle of 25.5. Then place each slanting end of this block on 

 cross-section paper and trace the area covered by each of the ends. What are the corresponding 

 areas covered by the two ends of the block ? How many times larger is one than the other ? 

 Which is the larger? If a beam of light 1 inch square falls at an angle of 72.5 and another 

 at 25.5, which will have the greater heating effect on 1 square inch of surface ? How many times 

 greater ? Why ? 



Additional problems. How are the facts of the above experiment related to the changes of seasonal 

 temperatures ? 



When the lights of automobiles or bicycles approach a gateway or doorway, are the upright posts or the 

 roadway between them the more brilliantly lighted ? Why ? 



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