某同学画的表示磁场B、电流I和安培力F的相互关系如图所示，其中正确的是 ( )
答案：D
题目分析：根据左手定则可知，A图中安培力方向应该向下，B图中安培力应该垂直于磁场斜向下，C图中磁场方向和电流方向在同一直线上，不受安培力作用，D图中安培力方向斜向左下方垂直于电流方向，故ABC错误，D正确．
故选D．
点评：左手定则中涉及物理量及方向较多，在应用过程中容易出现错误，要加强练习，增加熟练程度．
What do you usually use your cellphone for? Calling friends or sending them text messages? As technology develops，nowadays cellphones can do much more than that．They have become all-in-one cell-phones. A typical example is Apple’s phone.The touch-screen cellphone plays music，connects to the Web，sends emails and takes photos. More than 1 million Apple’s phones have been sold since it was sold in June. “Today’s young people enjoy using all kinds of digital functions，such as those of a music player，a camera and even a computer. An all-in-one cellphone is easy to carry. That is the goal of developing a technology to make our lives more convenient，simple and relaxed，said Professor Ding Shouqian at Nankai University． However, the all-in-one cellphones come with some problems. Users have complained that they are too complicated to use them, and that their battery life is too short. Cellphone producers say that they are working hard to make their phones even better. It is very convenient to use it. “We are trying to make the cellphones in a way that people can quickly move from phoning to taking pictures to listening to music, said Alastair Curtis, Nokia’s chief designer.“If you look at the Nokia 3250 model, it has a twisting(转动) bottom. So you twist it half a turn，and it’s in camera mode. You twist it another 90 degrees, and it’s in music player mode．”Japanese companies such as Toshiba and Fujitsu are also working to develop a new kind of battery for cellphones． If all the problems are solved in the future, all-in-one phones will change our lives for the better.
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