题干

2015•抚顺)如图所示,光线AO是通过凹透镜折射后射向水面的一条光线.请画出光线AO通过凹透镜前的入射光线、在水面的反射光线以及进入水中的折射光线的大致方向.

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解:平行于主光轴的光线经凹透镜折射后,其折射光线的反向延长线过焦点.据此作出光线AO通过凹透镜前的入射光线;

过入射点垂直界面作出法线,在空气中法线的另一侧作出反射光线,注意反射角等于入射角;

在水中法线的另一侧作出折射光线,注意折射角小于入射角,如图所示:

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        Franklin D. Roosevelt, U.S. President at the time, believed thatthe Allies (联盟) should plan for peace before the war ended. On December 1, 1943, Roosevelt, Britain's Winston Churchill and Joseph Stalin from Soviet Union agreed to start anorganization for world peace.

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        During the next year and a half, the idea of such anorganisation was debated around the world. Then came the big day. On April 11,1945, the first international meeting of the United Nations took place in SanFrancisco. The goal of the meeting was to write the U.N. Charter (宪章). All of thefifty-one nations at the meeting had their own ideas to offer for the Charter.

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