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中国教育在线
9 年
初二(八年级)上学期物理知识点:透镜及其应用 ...
2、光心:同常位于透镜的几何中心;用“O”表示。 3、焦点:平行于凸透镜主光轴的光线经凸透镜后会聚于主光轴上一点,这点叫焦点;用“F”表示。
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