磁场的磁感应强度大小在
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmn%3E100%3C%2Fmn%3E%3Cmtext%3E%CE%BCT%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
(
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmtext%3E%CE%BCT%3C%2Fmtext%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmsup%3E%3Cmrow%3E%3Cmn%3E10%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmo%3E%E2%88%92%3C%2Fmo%3E%3Cmn%3E6%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmsup%3E%3Cmtext%3ET%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
)之内,对人体是安全的。赤道上有一用于轻轨电车引电的载流长直导线,沿东西方向水平延伸,导线中通有大小为 150A,方向由东向西的电流。已知通电长直导线周围的磁感应强度大小的计算公式为
![](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%3Cmi%3Ek%3C%2Fmi%3E%3Cmfrac%3E%3Cmi%3EI%3C%2Fmi%3E%3Cmi%3Er%3C%2Fmi%3E%3C%2Fmfrac%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
,式中I为导线上的电流大小,r为某点距导线的距离,
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3Ek%3C%2Fmi%3E%3Cmo%3E%E2%89%88%3C%2Fmo%3E%3Cmn%3E1.3%3C%2Fmn%3E%3Cmo%3E%C3%97%3C%2Fmo%3E%3Cmsup%3E%3Cmrow%3E%3Cmn%3E10%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmo%3E%E2%88%92%3C%2Fmo%3E%3Cmn%3E6%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmsup%3E%3Cmtext%3ET%3C%2Fmtext%3E%3Cmo%3E%E2%8B%85%3C%2Fmo%3E%3Cmtext%3Em%2FA%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
,赤道表面附近的地磁场约为
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmn%3E5.0%3C%2Fmn%3E%3Cmo%3E%C3%97%3C%2Fmo%3E%3Cmsup%3E%3Cmrow%3E%3Cmn%3E10%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmo%3E%E2%88%92%3C%2Fmo%3E%3Cmn%3E5%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmsup%3E%3Cmtext%3ET%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
。下列说法正确的是 ( )
- A、在导线的正下方,电流产生的磁场方向自南向北
- B、在导线正下方1.5m 处,电流产生的磁感应强度大小约为13μT
- C、若考虑地磁场的影响,在导线的正上方1.5m 处,磁场对人体是安全的
- D、若考虑地磁场的影响,在导线的正下方1.5m 处,磁场对人体是安全的