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小明看到家中日光灯管的两端各有 一圈黑色(如图甲所示),从外面擦 怎么也擦不掉,他觉得奇怪,于是向 爸爸请教,爸爸让他在一支长试管内 装入少量的碘粉,塞上底部悬挂了少 量棉线的橡皮塞,用酒精灯慢慢加 热,如图乙所示. (1) 加热时小明看到碘粉没有熔化就有紫色的烟雾升起,这是 _______ 过程,需要 _______ 热,同时发现棉线上好像下了紫色的霜,这是 _______ 过程 (2) 一段时间后,小明看到离试管底一段距离处,出现了一圈紫色的堆积物,这是碘而形成的,并且时间越长,堆积越多.由此小明推断日光灯管上的黑圈是钨丝先 _______ 后 形成的. (3) 经过这个探究,小明明白了高压电线上凝结的厚冰柱(如图丙所示)经过一个无雨、无雪的寒冷夜晚变粗的原因,你认为下列对原因分析合理的是 ( ) A .白天温度高,电线和冰柱遇热膨胀 B .空气中的水蒸气遇到厚冰柱变成了冰 C .空气中的水珠遇到厚冰柱后凝固成冰 D .空气中的二氧化碳遇到厚冰柱变成了干冰
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