题目练习1:电荷线密度为λ的无限长带电直线的电-|||-场强度分布-|||-dfrac (lambda )(2pi {varepsilon )_(0)}-|||-(B dfrac (lambda )(2pi {{varepsilon )_(0)}^r}-|||-○ dfrac (lambda )(2pi r)-|||-D dfrac ({{u)_(0)}^lambda }(2pi r)题目解答答案