题干

关于磁感应强度,下列说法正确的是()

A:一小段通电导体放在磁场A处,受到的磁场力比B处的大,说明A处的磁感应强度比B处的磁感应强度大

B:由B=F/IL可知,某处的磁感应强度大小与放入该处的通电导线所受磁场力F成正比,与导线的IL成反比

C:一小段通电导体在磁场中某处不受磁场力作用,则该处磁感应强度一定为零

D:小磁针N极所受磁场力的方向就是该处磁感应强度的方向

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D

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    A great invention by an 18-year-old high school student grew out of a simple problem most teenagers meet with.

    “I'm a teenager and I have a cellphone and my cellphone battery always dies,so I was really looking for a way to improve energy storage,” Eesha Khare said on Tuesday. “That's how I came across the super capacitor.”

    The teenager who came from California, and graduated from high school last week,won a $50,000 prize on May 17,2013 at the Intel International Science and Engineering Fair for creating a device that can store enough energy to charge a cellphone in 20 to 30 seconds.

    “It charges very quickly and can store a lot of energy,” Khare said. “The cool thing is that it's a lot thinner than one strand of hair.”

    Khare hasn't used her invention to recharge a cellphone yet,but she used it to power a light-emitting diode (LED) in order to show its capability(容量). If used on cellphones,the supercharger would slide on to the phone's battery to juice it up in a matter of seconds. The technology isn't available to consumers yet,and it could be years until it is.

    At an Intel event in Phoenix,Khare won the Intel Foundation Young Scientist Award,taking second place overall in the world's largest high school science research competition. She beat out more than 1,600 finalists from 70 countries. She said that she has been approached by several companies to continue her research,but she is now focused on attending Harvard University in autumn.

    “Right now,just my education,but hopefully we'll see what happens in the future,” she said about her plans. “I have a lot of interests,so we'll see what I do in the future.”