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?
6.1 縱波 Sonar, Seismic Waves and Ultrasound
6.2 聲速 Bulk Modulus：B 容積彈性模數
氣體、液體與固體中的聲速
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
6.3 行進聲波 Displacement amplitude of an air element 位移
位移與壓力
例二 人耳耳膜可感知的最大與最小壓力差與位移
destructive interference 6.4 干涉 光程差和相位差 Fully constructive destructive interference
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
6.5 強度與聲級 The Sound Level • 通過單位面積之平均功率 Intensity
強度隨距離之變化
分貝 • The Decibel Scale
聲級β
例四 The WHO –the loudest concert The Who: 120 dB 鑽孔機 : 92 dB I1: I2 = 630!
6.6 音樂聲源 pipe
駐波與共振
橫笛、雙簧管和薩克斯風 Playing the same note 音符
例五 紙筒的聲音 (a) 靠近耳朵 (b) 離開耳朵
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.
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.
6.7 Beats 拍 - II
7.8 The Dopper Effect (a) Detector moving; source stationary
頻率變化 –(a)
Source moving; detector stationary
頻率變化 – (b) (general) (low speed)
6.9 超聲速–震波 Mach Cone/Shock Wave Mach Number
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
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
6.10光的都卜勒效應 magnitude
例八 The M87 galaxy 200 ly
超大黑洞
敬請期待 物理 VII–溫度與熱