人教版高中《物理选修3-1》第108面“问题与练习”第5题是这样的:电视显像管上的图像是电子束打在荧光屏的荧光点上产生的.为了获得清晰的图像,电子束应该准确地打在相应的荧光点上.电子束在飞行过程中受到地磁场的作用,会发生我们所不希望的偏转.下面我们来估算地磁场对显像管成像的影响,估算中认为电子束在被加速后飞向荧光屏的过程中速率不再改变,电子束的加速电压约为 U=2×10~4V,电 PEP High School “Physics Elective 3-1” No. 108 “Problems and Practices” The fifth problem is this: The image on the TV picture tube is generated by the electron beam hitting the fluorescent point of the screen. To obtain a clear In the image, the electron beam should hit the corresponding fluorescent point accurately. The electron beam is affected by the geomagnetic field during the flight, and we will experience undesired deflection. Here we estimate the influence of the geomagnetic field on the imaging of the picture tube. It is believed that the speed of the electron beam after it is accelerated to the fluorescent screen is no longer changed. The acceleration voltage of the electron beam is approximately U=2×10~4V.