How does a horseshoe bat detect a moth in total darkness?

Presentation on theme: "How does a horseshoe bat detect a moth in total darkness?"— Presentation transcript:

1 How does a horseshoe bat detect a moth in total darkness?
6 聲波 How does a horseshoe bat detect a moth in total darkness?

2 6.1 縱波 Sonar, Seismic Waves and Ultrasound

3 6.2 聲速 Bulk Modulus：B 容積彈性模數

4 氣體、液體與固體中的聲速

5 例一 聲源的方向 空氣中 水中 在水中由90°傳來之聲波將造成誤判 apparent angle

6 6.3 行進聲波 Displacement amplitude of an air element 位移

7 位移與壓力

8 例二 人耳耳膜可感知的最大與最小壓力差與位移

9 destructive interference
6.4 干涉 光程差和相位差 Fully constructive destructive interference

10 例三 圓上有幾個完全建設性 干涉點？ (a) ΔLP1= 0, ΔLP2= D =1.5λ
例三 圓上有幾個完全建設性 干涉點？ (a) ΔLP1= 0, ΔLP2= D =1.5λ φP1 = 0, φP2= (1.5λ/λ)2π= 3π (b) N = 6 around the circle

11 6.5 強度與聲級 The Sound Level • 通過單位面積之平均功率 Intensity

12 強度隨距離之變化

13 分貝 • The Decibel Scale

14 聲級β

15 例四 The WHO –the loudest concert
The Who: 120 dB 鑽孔機 : 92 dB I1: I2 = 630!

16 6.6 音樂聲源 pipe

17 駐波與共振

18 橫笛、雙簧管和薩克斯風 Playing the same note 音符

19 例五 紙筒的聲音 (a) 靠近耳朵 (b) 離開耳朵

20 Beat Frequency For the difference frequency you can just say that you get a minimum when the modulating term reaches zero, which it does twice per cycle.

21 6.7 Beats 拍 For the difference frequency you can just say that you get a minimum when the modulating term reaches zero, which it does twice per cycle.

22 6.7 Beats 拍 - II

23 7.8 The Dopper Effect (a) Detector moving; source stationary

24 頻率變化 –(a)

25 Source moving; detector stationary

26 頻率變化 – (b) (general) (low speed)

27 6.9 超聲速–震波 Mach Cone/Shock Wave Mach Number

28 例六 玩具火箭發射聲波 f = 1250Hz v = 242m/s (a) f ’ 偵測器接收的頻率
(b) f ’’ 火箭偵測到反射波的頻率

29 例七 蝙蝠和飛蛾 (a) fm when fbd = 83kHz (b) fbe when fbd = 83kHz
Vb = 9 m/s vm= 8 m/s (a) fm when fbd = 83kHz (b) fbe when fbd = 83kHz

30 6.10光的都卜勒效應 magnitude

31 例八 The M87 galaxy 200 ly

32 超大黑洞

33 敬請期待 物理 VII–溫度與熱