题干

小明同学用镜头焦距为10cm的普通照相机给小芳同学拍照,按快门时不小心将中指的指尖触摸到镜头一小部分,这张照片上能不能有小明同学指尖清晰像?请说明理由.

 

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答案(点此获取答案解析)

答:不能;因为照相机相当于一个凸透镜,它是根据物体位于凸透镜二倍焦距之外成倒立缩小实像的原理而工作的,由于小明同学的指尖触摸镜头时,指尖位于凸透镜一倍焦距之内成正立放大的虚像,所以不会在底片上得到指尖清晰的像.

同类题5

I’m an American . Years ago,I traveled to the north of Thailand. I  the heat,the noisy streets,the busy markets and the smell of Thai dish es. I enjoyed my     there very much. However,there is one thing that I wish I hadn’t done.

One day,I set off from my hotel to a temple that    me. It was a very    day. As I walked past some buildings,I glanced between two    buildings. There,an old woman in traditional clothing  on the dusty rubble(碎石).The terrible thought crossed my mind that she might be    .Feeling quite helpless,I  her. Her face was sunkissed. She looked quite beautiful but very ill. I    reached into my pocket to find some   .Then I pushed it into her hand. It was enough for her to   for a few months. At this moment,she opened her large,brown eyes and  the prize I’d given he r. I felt like the “  stranger”.

  a common language,she looked at me with the wisdom and pity that could burn into a soul. She weakly   the money. She stood up and walked away. I was  ,with the money in my hand. It took me at least a kilometer of walking to  I was quite the fool. She didn’t need money.  she needed shade,a bottle of water or just some comfort. She was the one who taught me a good  .

That evening,I sat thinking over my “kindness”. This b eautiful woman made me know that not everyone would  someone else’s money. We should be kind to others,but we should choose the right way.