3.
如图甲为研究光电效应的装置示意图,图乙为垂直于磁场的截面,该装置可用于分析光电子的信息。竖直放置足够大且接地、逸出功为
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3EW%3C%2Fmi%3E%3Cmn%3E0%3C%2Fmn%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
的金属板P,金属板右侧分布有磁感应强度大小
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3EB%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmfrac%3E%3Cmrow%3E%3Cmsqrt%3E%3Cmrow%3E%3Cmi%3Em%3C%2Fmi%3E%3Cmsub%3E%3Cmi%3EW%3C%2Fmi%3E%3Cmn%3E0%3C%2Fmn%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3C%2Fmsqrt%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmi%3Ee%3C%2Fmi%3E%3Cmi%3ER%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
的匀强磁场,方向平行于金属板水平向里。磁场中有足够长且接地、半径为R的金属圆筒Q,其轴线与磁场方向平行,筒Q横截面的圆心O到金属板的距离为
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmn%3E3%3C%2Fmn%3E%3Cmi%3ER%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
。当频率
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3E%CE%BD%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmfrac%3E%3Cmrow%3E%3Cmn%3E27%3C%2Fmn%3E%3Cmsub%3E%3Cmi%3EW%3C%2Fmi%3E%3Cmn%3E0%3C%2Fmn%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E2%3C%2Fmn%3E%3Cmi%3Eh%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
的入射光照射到板P右表面时,表面各点均逸出大量速率不同、沿空间各个方向运动的电子。已知电子电量为e、质量为m,普朗克常量为h,板P和筒Q 始终不带电,忽略相对论效应,不计电子重力和电子之间相互作用。
![](http://tikupic.21cnjy.com/ct20241o/7b/ec/7bec026aa2d0a43fcafab28e93bc3f1e.png)