题干

处于激发状态的原子,在入射光的电磁场的影响下,从高能态向低能态跃迁,两个状态之间的能量差以辐射光子的形式发射出去,这种辐射叫做受激辐射.原子发生受激辐射时,发出的光子频率、发射方向等,都跟入射光子完全一样,这样使光得到加强,这就是激光产生的机理.那么,发生受激辐射时,产生激光的原子的总能量En、电势能Ep、电子动能Ek的变化情况是()

A:Ep增大、Ek减小、En减小

B:Ep减小、Ek增大、En减小

C:Ep增大、Ek增大、En增大

D:Ep减小、Ek增大、En不变

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答案(点此获取答案解析)

B

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阅读理解

    One morning while Officer Vogel was on his coffee break in a restaurant, a man ran in a yelled. "Officer! A little kid is driving a car down the street!"

    He ran out at once and saw a car going slowly—about 25 miles an hour—but it was going very straight. He jumped into his police car and followed it. When the car was stopped, Officer Vogel looked inside. The driver was a little boy. His name was Rocco Morabiro and was 5. In the back seat was his two-year-old sister. Both children wen crying.

    "I want my mummy!" the boy cried."But she can't get here. I have the car." Then he had an idea."Just a minute." He told Officer Vogel."I can drive. I'll go to get her."

    "No!" Officer Vogel said. "You stay with me!" Then he drove them to the police station and he called their mother. They had many questions for Rocco. The first question was: "Where did you get the car keys?"

    Rocco said. "From the top of the refrigerator."At seven that morning Rocoo's father was work and his mother was sleeping, Rocco saw the keys on top of the refrigerator. He climbed on a chair, and took the keys.

    Rocco got into the car and started the engine (引擎). When Rocco's sister heard the engine she ran to the car and cried. She wanted to go with him.

    It was 7 a.m.—rush hour—so there was much traffic. Rocco drove one mile in heavy traffic. Then Officer Vogel stopped him.

    Newspapers and TV stations heard about Rocco, and a lot of reporters went to his house. A reporter asked Rocco, "What do you want to be when you grow up?"

    "A truck driver,"he said, smiling.