利用磁场对通电导体产生力的作用来制造的电器是（　　）

如图所示，下端封闭且粗细均匀的“7”型细玻璃管，竖直部分长l=50cm，水平部分足够长，左边与大气相通，当温度t₁=27℃时，竖直管内有一段长为h=10cm的水银柱，封闭着一段长为l₁=30cm的空气柱，外界大气压始终保持P₀=76cmHg，设0℃为273K，试求：

①被封闭气柱长度为l₂=40cm时的温度t₂；

②温宿升高至t₃=177℃时，被封闭空气柱的长度l₃．

一物体做匀变速直线运动，某时刻速度的大小是3m/s，1s后的速度大小变成了8m/s，在这1s内该物体的（   ）

     Mr. Jackson is a teacher of science in a middle school. His students like his classes because his classes are very interesting. They can learn a lot in his class. The students can make（制作）many things. His little son Val also likes making things. He makes lots of machines（机器）, such as a machine like a man. It can do the job that is dangerous（危险的）for people to do. He says, “I want to be a scientist.”
根据短文内容，选择正确答案。