A′B′是物体AB经过凸透镜所成的像，CC′是主光轴，在图中大致的位置上画出透镜和焦点．
连接物像的端点A、A′并延长与主光轴交于O点，O点为凸透镜的光心，过O点垂直主光轴作出凸透镜；
从A点平行于主光轴作一条入射光线，交与凸透镜与E点，连接A′E并延长交于主光轴 F点，F点为凸透镜的一个焦点，EF为入射光线AE的折射光线，在凸透镜的左侧对称的作出另一焦点F，如图：
Mr. White works in an office. He’s able and can easily deal with all kinds of matters. 60 . Of course he’s often busy and has no time to do the housework. His wife does all at home. Last Friday, their daughter was hurt in a traffic accident and had to be in hospital. Mrs. White had to look after her there and she couldn’t go home to take care of the house and her husband. When Mr. White was at home alone, he never cooked meals. 61 . Yesterday morning, before Mr. White got up, the telephone rang. 62 . His friend told him to write down an important telephone number. But he could find neither a pen nor a piece of paper. At this moment, he found there was much dust (灰尘) on the table and he wrote the number on it with his forefinger (食指). 63 . In the afternoon, his wife came back to look for a sweater for her daughter. When Mr. White returned from work and saw his wife cleaning the table, he rushed to her while shouting, “Stop!” But it was too late!
|