题干

 在“探究凸透镜成像规律”的实验中,各组使用相同焦距的凸透镜进行实验.
(1)小华所在的小组实验操作规范,测量准确,该小组实验记录如下表:

请你根据上表信息,求出凸透镜的焦距f=____ cm.
(2)小华所在的小组把蜡烛放在该凸透镜的焦点上,凸透镜固定不动,将光屏向远离凸透镜的方向移动的过程中,在光屏上观察到的现象是____ .
(3)若烛焰、凸透镜、光屏放在适当位置时恰好在光屏上成清晰的像,当凸透镜位置不变,烛焰向远离凸透镜方向移动一小段距离时,为了在光屏上再成清晰的像,光屏应向____ (远离/靠近)凸透镜方向移动适当的距离.
(4)对于焦距相同的凸透镜,一个物距应该对应唯一的像距,但从各小组汇报数据中发现,物距均为12.00cm时,有三个小组所测像距分别为23.00cm、24.00cm、26.00cm.若他们的数据差别不是因为长度测量误差导致的,你认为出现这种情况的操作原因是____ 

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答案(点此获取答案解析)

8,大小不变的光斑,靠近,光屏上没有成清晰的像就开始测量

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    Most people say that most people have not more than 30 friends at any given time, and 400 over the whole of their lives. However, on social networking sites, most users have about 150 friends. If these numbers are correct, then friendship means different things in different situations.

    Also, there are no rules about friendship. There are no instructions about how to make friends, how to keep friendships going, and how to finish friendships if we want to move on. People have very different opinions about this: some people would die for their friends and they value them more than family. Others say that friends are temporary, only there to help each other until they are no longer needed. If people with such different views become friends, this can lead to problems.

    Because of these different definitions of friendship, it is easy to be unhappy about our friendships. We may want them to be deeper or closer, or we may want to have more friends in our lives. Sometimes we simply do not have the time to develop our friendships, or we fear we have left it too late in life to start. If we move to another country or city, we have to find ways, to make new friends again.

    This dissatisfaction shows us how important friendships are for most of us. We should not think that it could be too late to build friendships. We also need to understand that the need to be around other people is one that is shared by many. Therefore, we should not be too frightened about starting to talk to people who in the future may become our friends: it is likely that they too would like to get closer to us. Remember what people say: strangers are friends we have not met yet.