物理功課不懂得做1 - Ans.fyi 參考答案

物理功課不懂得做1

2013-02-07 11:28 pm

9. 假設一人造衝星在太空中燃燒和爆炸，我們在地上可以看見的火焰，但郤聽不到爆炸的聲響。試解釋原因。

10 某歌手在大型足球場上演唱，舞台上安裝了一個大螢幕和數個揚聲器。坐在遠處的觀眾發現歌手的歌聲和螢幕顯示的畫面並不同步。試指出原因，並提議怎樣解決這個問題。 (小助手：考慮光和聲音在空氣中的速率。)

13 人類能製造的最低和最高可聽頻率是20 Hz和4450 Hz。
(a) find相應的波長範圍。已知聲音空氣中的速率是340 ms^-1。
(b) 人類嘴巴的闊度(4-5 cm)適宜把聲音傳播至廣闊的範圍嗎？試簡單解釋。

14 漁船使用聲納來探度和魚羣的位置。如果訊號在發出後約3 s從海底返回漁船，find海的深度。 (聲音在水中的速率1400 ms^-1)

18 屯門公園有人使用揚聲器高聲演奏音樂。
(a)假設你住在公園的對面，判斷這這些聲音是音樂還是噪音。
(b) 假設你是在公園跳舞的其中一人，判斷這這些聲音是音樂還是噪音。
(c) 假設你是該區的區議員，你會向政府作出甚麼建議來解決這個問題。

回答 (1)

天同

2013-02-08 12:17 am

✔ 最佳答案

9. Sound needs a medium (e.g. air) to propagate. Space has no air. Hence sound cannot travel through space.

10. Light travels much faster than sound in air. The vision of the singer thus arrives at the eyes of the audience much earlier than sound does.
Solution: install more louspeakers near the audience.

13. (a) Wavelength of 20 Hz wave = 340/20 m = 17 m
Wavelength of 4450 Hz = 340/4450 m = 0.0764 m (= 7.64 cm)
(b) The dimension of the human mouth is is shorter than the wavelength of the highest note that he can produce. It is not suitable to propagate sound in wide areas.

14. Distance travelled by the sonar signal (聲納訊號) = 1400 x 3 m = 4200 m
Depth of sea = 4200/2 m = 2100 m

18. This seems not a physics question.
Whether the sound is noise or music depends on very much human feeling.
Also, the recommendation given a District Board Member takes into consideration social factors and degree of acceptance by local residents. It is not purely a scientific decision.

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