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第13章 机械波
§13.1 机械波的产生和传播
§13.2 平面简谐波
§13.3 波的能量和能流
§13.4 波的干涉
§13.5 驻波
§13.6 多普勒效应
§13.1 机械波的产生和传播
Waves are of three main types:
电磁波 Electromagnetic waves
These waves require no material medium to exist. All electromagnetic
waves travel through a vacuum at the same speed c.
机械波 Mechanical waves
These waves are governed by Newton's laws, and they can exist only
within a material medium.
CAI
物质波 Matter waves
……
⑵ 介质⑴ 波源机械波产生的两个条件:
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弹性介质中传播的机械波
外力撤消物体 在力的作用下 形变 形变能够消失
弹性形变 弹性体具有弹性形变的物体
由弹性体组成的介质 弹性介质
振动状态的传播
质元
transverse wave横波 CAI
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CAI
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振动状态的传播
longitudinal wave纵波
CAI
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§18.2 平面简谐波 Plane Harmonic Waves
简谐振动具有时间周期性
周期 period T 频率 frequency f 角频率 angular frequency ω
波是振动状态在空间的传播
简谐波不但具有时间周期性,还具有空间周期性
用 来描述波的空间周期性波长 wavelength λ
它表示振动在一个周期 T 内所传播的距离
如果把单位时间内振动状态的传播距离称为波速 v
π
ωλ
λ
λ
2
=== f
T
v
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振动状态是由相位确定的
为了形象地描述波在空间的传播,通常把某一时刻振动
相位相同的各点的轨迹称为波面 wave surface
球面波
point source
平面波
波前(波阵面) Wave fronts波线
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