《信息的传递》单元测试题二（参考答案）

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8、TTOM: 0cm一、选择题1-14：D D C A C C A C D A A D D D二、填空题15电磁16增大 等于 3×1085.71“5.7亦可 17机械能 电磁波18紫外线 红外线 X射线 无线电波19增强 减弱20电磁波 激21 三、简答与实验题22(1)收音时机发出咔咔嚓嚓的声音。这是因为导线头在锉面上滑动时 ,产生了变化的电流 ,向空中激起了电磁波。2开启冰箱门时会听到收音机也发出“咔咔嚓嚓的声音23接收卫星传来的信号。光缆通信的主要优点：容量大 ,不怕雷击 ,不受电磁干扰 ,通信质量高 ,保密性好。(2)开、关日光灯时 ,产生了变化的电流 ,周围空间就存在电磁波 ,电视机接收以后 ,会在电视机画面上出现雪花点。四、阅读与计算题24C 3×108具有 三 微波炉的外壳用不锈钢等金属材料制成 ,可以阻