问题 选择题

平行单色光a垂直射向一半径为R的玻璃半球的平面,其截面如图所示,发现圆弧AB上只有

1
3
区域有光射出(不考虑光反射后的折射光线).若将a平行光换成b平行光,发现光从AB弧上射出的范围增大.下列说法正确的是(  )

A.玻璃半球对a光的折射率为2

B.b光在玻璃半球中的速度小于a光在玻璃半球中的速度

C.真空中,b光波长比a光波长短

D.如果a光照射一块金属板发生光电效应,那么b光照射同一金属板也一定能发生光电效应

答案

A、a光进入玻璃后射到圆弧AB上只有

1
3
区域有光射出,说明另外
1
3
区域的光发生了全反射,其临界角C=30°,由sinC=
1
n
得到,折射率n=2.故A正确.

    B、由题,b光从AB弧上射出的范围增大,说明b光的临界角大于a光的临界角,b光的折射率小于a光的折射率,由公式v=

c
n
分析可知,b光在玻璃半球中的速度大于a光在玻璃半球中的速度.故B错误.

    C、b光的折射率小于a光的折射率,由b光的频率小于a光的频率,由公式c=λf可知,真空中,b光波长比a光波长长.故C错误.

    D、由于b光的频率小于a光的频率,a光照射一块金属板发生光电效应,b光照射同一金属板不一定能发生光电效应.故D错误.

故选A

单项选择题

阅读下面短文,从短文后各题所给的四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项,并在答题卡上将该项涂黑。学科&网

Hundreds of people have formed impressions of you through that little device(装置) on your desk. And they’ve never actually   41   you. Everything they know about you   42   through this device, sometimes from hundreds of miles away.   43   they feel they can know you   44   from the sound of your voice. That’s how powerful the   45   is.

Powerful, yes, but not always   46  . For years I dealt with my travel agent only by phone. Rani, my faceless agent whom I’d never met   47  , got me rock-bottom prices on airfares, cars, and hotels. But her cold voice really   48   me. I sometimes wished to   49   another agent.

One morning, I had to   50   an immediate flight home for a family emergency. I ran into Rani’s office   51  . The woman sitting at the desk,   52   my madness, sympathetically jumped up. She gave me a   53   smile, nodded while listening patiently, and then printed out the   54   immediately. “What a wonderful lady!” I thought.

Rushing out   55   I called out over my shoulder, “By the way, what’s your name?” “I’m Rani,” she said. I turned around and saw a   56   woman with a big smile on her face waving to wish me a safe trip. I was   57  ! Why had I thought she was cold? Rani was, well, so   58  .

Sitting back in the car on the way to the airport, I figured it all out. Rani’s   59  ---her warm smile, her nods, her ‘I’m here for you’   60  ---were all silent signals that didn’t travel through wires.

48()

A. annoyed

B. interested

C. discouraged

D. confused

单项选择题