高压电线落地可能导致行人跨步触电,如图所示,设人的两脚MN间跨步距离为d,电线触地点O流入大地的电流为I,大地的电阻率为ρ,ON间的距离为R,电流在以O点为圆心、半径为r的半球面上均匀分布,其电流密度为
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3EU%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmi%3EE%3C%2Fmi%3E%3Cmi%3Ed%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmsub%3E%3Cmrow%3E%3Cmi%3EB%3C%2Fmi%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmsub%3E%3Cmsub%3E%3Cmrow%3E%3Cmi%3Ev%3C%2Fmi%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmsub%3E%3Cmi%3Ed%3C%2Fmi%3E%3C%2Fmath%3E)
, 已知电流密度乘以电阻率等于电场强度,该电场强度可以等效成把点电荷Q放在真空中O点处产生的电场强度。下列说法正确的是( )
![](http://tikupic.21cnjy.com/2022/05/10/f8/3a/f83a558aa68829535e09bdfcd2bb4d53_325x236.png)
- A、越靠近O点,电势越低
- B、两脚间距离越大,跨步电压一定越大
- C、等效点电荷Q的电荷量为
(k为静电力常量) - D、若M,N,O三点在一条直线上,图中两脚MN间跨步电压等于
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmfrac%3E%3Cmrow%3E%3Cmtext%3E%CF%81%3C%2Fmtext%3E%3Cmi%3EI%3C%2Fmi%3E%3Cmi%3Ed%3C%2Fmi%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E2%3C%2Fmn%3E%3Cmtext%3E%CF%80%3C%2Fmtext%3E%3Cmsup%3E%3Cmrow%3E%3Cmi%3ER%3C%2Fmi%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmsup%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3C%2Fmath%3E)