题目

完成下列光学实验要求：（1）“用平行光测凸透镜焦距”实验的实验原理是：__________________（2）如图所示是探究“凸透镜成像规律”实验示意图。①当蜡烛在a点时，像的特点是：__________________________________；②将蜡烛从a点移到b点，光屏不动。此时将凸透镜向哪个方向移动才能使像变的清晰且是放大的？________________________________。③在移动凸透镜的过程中，请具体说明怎样操作才能把凸透镜调到比较准确的位置______？ April 21 was the national memorial day ____ were killed in Yushu Earthquake on April 14 2010. A in honor of any one who           B in celebration of  those who C in memory of  whoever           D in charge of  no matter who