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“I like photography because it captures amazing things that you might not see again,” Timmy Walsh says. He takes pictures of flowers, sunsets and road signs. But those photos don't usually end up in a scrapbook(剪贴簿) or on his bedroom walls.
When Timmy was five, he found out that his aunt Bev had lung cancer. He wanted to do something to help her. His first idea was to sell his photos from a lemonade--type stand in front of his house in Pennsylvania. “My mom said it wouldn't work because we were not on a busy street,” Timmy explains.
His next idea was to have an art show. Timmy decorated his home with candles, flowers, and white lights. Then he arranged his photos. Timmy's mom, Sheila, remembers: “Our dining-room table was filled, the living room—everything was filled with photos.” Friends, family, and Timmy's teachers came to the show. He raised more than $300 for cancer research that night. Aunt Bev was “very happy and excited,” he says.
After a local newspaper wrote a story about Timmy's photos, a volunteer offered to help him set up a website. As people learned about his cause, called Camera for a Cure, Timmy began receiving invitations to sell his pictures at art galleries and fund-raisers. Since then, his work has appeared in more than 20 shows.
When Timmy is at a show, he greets each customer and talks about what he was thinking when he took his photos. And he always shares facts about lung cancer. Sometimes donations and sales are slow, but that doesn't bother him. “It doesn't matter how much money we made because we just raised awareness,” he says. Timmy knows that finding a cure for lung cancer will take time and effort. So Timmy will keep doing his part by shooting and selling photos of the things he sees.
时刻导线框的上边恰好与磁场的下边界重合(图中位置I)，导线框的速度为
经历一段时间后，当导线框的下边恰好与磁场的上边界重合时(图中位置II)，导线框的速度刚好为零。此后，导线框下落，经过一段时间回到初始位置I。则
