题干

白光经三棱镜折射后,光屏上自上而下出现了红、橙、黄、绿、蓝、靛、紫的色带,如图1所示,即玻璃对不同颜色光的折射程度不同,而凸透镜是利用光的____原理制成的光学元件.受此启发,小秋猜想:不同颜色的平行光,经同一个玻璃凸透镜后的会聚点(焦点)的位置应该不同.于是他选取某一个凸透镜,用红光和蓝光来进行如图2所示的实验,分别测量凸透镜的焦距,实验结果证明他的猜想果然是正确的,即同一个凸透镜,____(选填“红光”或“蓝光”)的焦距大一些

上一题 下一题 0.0难度 选择题 更新时间:2019-09-17 04:13:45

答案(点此获取答案解析)

折射,红光

同类题4

根据短文内容,选择最佳答案。

    Each summer,you hear news that some sports players are sent to hospitals because it is too hot. Our bodies can't be outside in the sun for a long time. So in hot summers,be careful about playing sports outside.

    Firstly,to play sports safely in hot weather,you must drink water. Sports drinks are great for athletes,but they have so much sugar that they'll dehydrate(使脱水)you more. However,drinking a few bottles of sports drinks will be good for you.

    Secondly,be sure to take enough breaks to let your body rest. If your coach doesn't let you take enough breaks in the heat,don't wait until you feel uncomfortable. Just be honest with your coach when you need breaks.

    Thirdly,when you have a break,don't sit in the sun. With the sun beating down on you,you'll only heat up and sweat(冒汗)more. Take a seat under a tree,or even better,go indoors for a little while. Cooling yourself down can help you stay active longer.

    Fourthly,remember that the earlier in the day you start your exercise,the cooler it will be. If you can start practice before the sun comes up,you have a few good hours to practise in the cool hours of the morning. Also,the earlier you practise,the earlier you can finish the exercise. If you need more practice time,come back to the field later in the evening,when the sun is setting.

    Last but not least,you should watch what you eat. Eat food which is high in water,starch(淀粉)and carbonhydrate(糖类),but be sure to get a good balance in your diet.

    As long as you pay attention to the above,playing sports safely in the heat isn't a difficult thing.