所用的时间（天数）

10

11

12

13

通过公路l的频数

20

40

20

20

通过公路2的频数

10

40

40

10

Then

    Once upon a time, people spent lots of time at home on weekends. Then, new inventions changed the weekends.

◆People used electric(电动的) streetcars to travel in cities. On weekends, they rode the streetcars to parks. Young people liked roller coasters(过山车).

◆The first movie lasted only one minute. Soon movies lasted longer. In the 1920s, movie theaters sold millions of tickets each week. In 1927, movies eventually(最终) had sound. Sometimes, people stayed at home instead, and listened to another new invention — radio.

◆People in cities worked indoors during the week, so they wanted to be outdoors on weekends. Bicycling became a popular activity.

Now

    With more time, money and inventions, people have much more choices.

◆They can visit large parks like Disney World and ride modern roller coasters that go higher and faster than ever before.

◆They can choose from lots of different movies at a multiplex (a building with many movie theaters) or watch a video at home.

◆Many people jog(慢跑), cycle, work out at the gym, or play sports. Others turn on their TV and watch sports.

物体到凸透镜的距离/cm

光屏上像到凸透镜的距离/cm

光屏上像

的大小

40

13.5

缩小

30

15

缩小

20

20

等大

15

30

放大

10

光屏上没有像

8

光屏上没有像