Ch12

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‫ﺍﻟﻔﺼل ﺍﻟﺜﺎﻨﻲ ﻋﺸﺭ‪ :‬ﺍﻷﻤﻭﺍﺝ‬

‫ﺍﻟﻔﺼﻞ ﺍﻟﺜﺎﻧﻲ ﻋﺸﺮ‬

‫ﺍﻷﻣﻮﺍﺝ‬ ‫)‪(Waves‬‬

‫‪ 1-12‬ﺘﻤﻬﻴﺩ‪:‬ﺍﻟﺤﺭﻜﺔ ﺍﻟﻤﻭﺠﻴﺔ )‪(Wave Motion‬‬ ‫ﺩﺭﺴﻨﺎ ﻓﻲ ﺍﻟﻔﺼل ﺍﻟﻌﺎﺸﺭ ﺍﻟﺤﺭﻜﺔ ﺍﻻﻫﺘﺯﺍﺯﻴﺔ ﻷﺠﺴﺎﻡ ﺍﻟﻤﺭﻨﺔ‪ ،‬ﻜﺠﺴﻡ ﻤﺭﺒﻭﻁ ﺒﺯﻨﺒﺭﻙ ﺃﻭ ﺒﻨﺩﻭل‬ ‫ﺒﺴﻴﻁ‪ ،‬ﻭﺤﺩﺩﻨﺎ ﺨﻭﺍﺼﻬﺎ ﺍﻷﺴﺎﺱ ﻤﻥ ﺩﻭﺭ ﻭﺘﺭﺩﺩ ﻭﻁﺎﻗﺔ‪ .‬ﻭﻨﺩﺭﺱ ﻓﻲ ﻫﺫﺍ ﺍﻟﻔﺼل ﻜﻴﻑ ﺘﻨﺘﻘل‬

‫ﺍﻫﺘﺯﺍﺯﺍﺕ ﺠﺴﻡ ﻤﻥ ﻨﻘﻁﺔ ﻷﺨﺭﻯ ﻓﻲ ﻭﺴﻁ ﻤﺸﻜﻠﺔ ﻤﻭﺠﺔ ﻤﻨﺘﺸﺭﺓ ﻓﻴﻪ‪ .‬ﻭﺘﻌﺘﺒﺭ ﺃﻤﻭﺍﺝ ﺍﻟﻤﺎﺀ ﺍﻟﺘﻲ‬ ‫ﺘﺘﺸﻜل ﻋﻨﺩ ﺴﻘﻭﻁ ﺤﺠﺭ ﻓﻲ ﺒﺭﻜﺔ ﻤﺎﺀ ﺴﺎﻜﻨﺔ ﻤﺜﻼ ﺒﺴﻴﻁﺎ‬

‫ﻭﻭﺍﻀﺤﺎ ﻟﻸﻤﻭﺍﺝ ﺍﻟﺘﻲ ﺘﻅﻬﺭ ﻓﻲ ﻤﺠﺎﻻﺕ ﺸﺘﻰ ﻓﻲ ﺍﻟﻁﺒﻴﻌﺔ‪.‬‬ ‫ﻓﻬﻨﺎﻙ ﺍﻷﻤﻭﺍﺝ ﺍﻟﺼﻭﺘﻴﺔ ﺍﻟﺘﻲ ﺘﺒﺩﺃ ﻓﻲ ﺍﻷﻭﺘﺎﺭ ﺍﻟﺼﻭﺘﻴﺔ ﻟﻁﻔل‬

‫ﺼﻐﻴﺭ ﻋﻨﺩﻤﺎ ﻴﺒﻜﻲ ﻓﺘﻨﺘﺸﺭ ﺒﻭﺍﺴﻁﺔ ﺫﺭﺍﺕ ﺍﻟﻬﻭﺍﺀ ﺍﻟﻤﺠﺎﻭﺭﺓ‬

‫ﻟﺘﺼل ﻷﺫﻥ ﺃﻤﻪ ﺍﻟﻤﺴﻜﻴﻨﺔ ﺍﻟﻨﺎﺌﻤﺔ ﻓﻴﻭﻗﻅﻬﺎ‪ ،‬ﻭﻫﻨﺎﻙ ﺍﻷﻤﻭﺍﺝ‬ ‫ﺍﻟﻜﻬﺭﻤﻐﻨﺎﻁﻴﺴﻴﺔ )ﺍﻟﻀﻭﺀ( ﻜﺎﻟﺘﻲ ﺘﺼﺩﺭ ﻋﻥ ﻫﻭﺍﺌﻲ ﻤﺤﻁﺔ ﺇﺭﺴﺎل ﻨﺎﻗﻠﺔ ﺒﺭﺍﻤﺞ ﺍﻹﺫﺍﻋﺔ ﻭﺍﻟﺘﻠﻔﺎﺯ‪،‬‬ ‫ﻭﻏﻴﺭﻫﺎ‪ .‬ﻭﻓﻲ ﻜل ﺍﻟﺤﺎﻻﺕ ﻓﻬﻨﺎﻙ ﻤﺼﺩﺭ ﻟﻠﻤﻭﺠﺔ‪ ،‬ﻜﻴﺩ ﺸﺨﺹ ﻴﻬﺯ ﺤﺒﻼ ﺃﻭ ﻴﻀﺭﺏ ﻋﻠﻰ ﻭﺘﺭ‬

‫ﻋﻭﺩ‪ ،‬ﺃﻭ ﻨﻔﺦ ﺭﺍﻋﻲ ﻓﻲ ﻗﺼﺒﺔ ﻫﻭﺍﺌﻴﺔ )ﻨﺎﻱ(‪ ،‬ﺃﻭ ﺍﻫﺘﺯﺍﺯ ﺇﻟﻜﺘﺭﻭﻥ ﻓﻲ ﻫﻭﺍﺌﻲ‪ .‬ﺃﻤﺎ ﻀﺭﻭﺭﺓ ﻭﺠﻭﺩ‬ ‫ﻭﺴﻁ ﻨﺎﻗل )ﺫﺭﺍﺕ ﺍﻟﻬﻭﺍﺀ ﺃﻭ ﻤﺎﺩﺓ ﻭﺘﺭ ﺍﻟﻌﻭﺩ( ﻓﺘﻌﺘﻤﺩ ﻋﻠﻰ ﻨﻭﻉ ﺍﻟﻤﻭﺠﺔ‪ ،‬ﻓﺒﻌﻀﻬﺎ ﻻﻴﻨﺘﻘل ﻤﻥ ﻨﻘﻁﺔ‬

‫ﻷﺨﺭﻯ ﺇﻻ ﺇﺫﺍ ﻭﺠﺩ ﻤﻥ ﻴﺤﻤﻠﻬﺎ ﻭﺘﺩﻋﻰ ﺃﻤﻭﺍﺠﺎ ﻤﻴﻜﺎﻨﻴﻜﻴﺔ )‪ ،(mechanical waves‬ﻭﻫﻨﺎﻙ ﺃﻤﻭﺍﺝ‬ ‫ﻻﺘﺤﺘﺎﺝ ﻟﻭﺴﻁ ﻨﺎﻗل ﻫﻲ ﺍﻷﻤﻭﺍﺝ ﺍﻟﻜﻬﺭﻤﻐﻨﺎﻁﻴﺴﻴﺔ )‪ (electromagnetic waves‬ﻭﺘﻨﺘﺞ ﻋﻥ‬

‫ﺍﻫﺘﺯﺍﺯ ﻤﺠﺎل ﻜﻬﺭﺒﺎﺌﻲ ﻭﺁﺨﺭ ﻤﻐﻨﺎﻁﻴﺴﻲ‪ .‬ﻭﻨﻅﺭﺍ ﻷﻨﻨﺎ ﻻ ﻨﺩﺭﺱ ﺍﻟﻜﻬﺭﺒﺎﺀ ﻭﺍﻟﻤﻐﻨﺎﻁﻴﺴﻴﺔ ﻓﻲ ﻫﺫﺍ‬ ‫‪295‬‬


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