ideological and theoretical qualities and practical working ability, and strive to build a contingent of league cadres with positive work style and high quality. Hold a regular meting of the party secretary every fortnightly, arrange the work of the regiment, fedback the student information. Focus on training junior high school, junior high school secretary of the regiment branch to enable them to raise A firm political conviction, diligent and diligent learning spirit and practical and innovative work style.声现象复习知识梳理一、声音的产生和传播1、声音的产生:声音是由于 而产生的 一切发声的物体都在 , 叫声源。2、声音的传播A. 传声的介质: 、 、 B. 不能传声C. 声波:声音在介质中是以 的形式传播的 D. 声速 ① 一般情况下,声音在 中传播最快, 中传播最慢; ② 在空气中,150C 时,声音传播的速度 ; ③ 声速与 有关; ④ 声速的测定:原理: ⑤ 有关声速的计算:发声者要想听到自己的回声,障碍物到听者的距离至少为 m。二、乐音的三要素: 1. 音调:指声音的 ,它是由发声体振动的 决定的, 频率越 ,音调越 ;2. 响度:指声音的 ,它跟发声体振动的 有关,振幅越 ,响度越 ;3. 音色:指不同发声体声音特色,不同发声体在音调和响度相同的情况下, 音色是不同的; 三、噪声的危害和控制: 1. 从物理学角度看,噪声是指 ;从环境保护的角度噪声是指 。人们用分贝(dB)来划分声音等级;听觉下限 dB;为保护听力应控制噪声不超过 90dB;为保证工作学习,应控制噪声不超过 70dB;为保证休息和睡眠应控制噪声不超过 50dB 。 2. 减弱噪声的方法: 防止噪声的 (在 减弱) 阻断噪声的 (在 减弱) Strengthen the team connection, strengthen the knowledge education among the students (especially the first grade students), and promote the formation of good school spirit with the influence of the league members. All League branches should start with recommending outstanding students as the development objects of the League, take amateur league schools as the...