如图所示,一条红色光线和另一条紫色光线,以不同的角度同时沿不同的半径方向射入同一块半圆形玻璃砖,其透射光线都是由圆心O点沿OC方向射出.则可知 ( )
A．AO是红光,它穿过玻璃砖所需时间较长
B．BO是红光,玻璃砖对它的折射率较小
C．AO是紫光,它穿过玻璃砖所需时间较长
D．BO是紫光,它穿过玻璃砖所需时间较短
BC
本题考查光的折射及光在介质中的速度.由图及折射定律知,玻璃对AO的折射率大,对BO的折射率小.由于玻璃对红光的折射率小,对紫光的折射率大,所以BO为红光,AO为紫光.光在介质中的传播速度为
,可知红光在玻璃中的速度大于紫光在玻璃中的速度.由
知,红光比紫光穿过玻璃所需的时间短.故正确选项为BC.
Ellen Parker was worried about her health. She could not walk very quickly and it was difficult for her to climb stairs（爬楼梯）. She was soon out of breath.（气喘吁吁） “I think I had better go to the doctor, ” she thought. She went to the doctor and told him her problem. “I’m not at all surprised, ”he said. “It’s obvious （明显的）what your problem is.” He examined her and then gave her some advice.“If you don’t do what I say, Mrs. Parker,” he said. “You will have a heart attack（心脏病）. It could kill you.” Ellen was very worried as she left the doctor’s. She knew that she had to take his advice but that would not be easy and it would take time. The next day she went shopping. The first shop she went into was a butcher’s shop（肉店）. “I’d like ten pounds of steak (大块肉片), please,” she said. “Certainly, madam,” the butcher(屠夫) answered and went into the cold room and found a large piece of steak. He brought the huge piece of meat back into the shop and placed it on the scale(秤). “That’s just ten pounds,” he said. “That’s big enough,” Mrs. Parker said. The butcher worked out(计算) the price. “At $ 4.99 a pound that will be $ 49.90, please. Would you like me to cut it into small pieces for you?” “Oh, I don’t want to buy the meat,” Mrs. Parker said. “If you don’t want to buy it,” the butcher said angrily, “Why did you ask me to get it for you?” “My doctor told me that I am overweight (超重的)and have to lose ten pounds. I wanted to see what ten pounds of flesh looked liked.” 小题1:. Why did Ellen Parker visit the doctor?
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