U=0-|||-(B) E=0 . =dfrac (q)(2pi {varepsilon )_(0)a}-|||-(C) =dfrac (q)(2pi {varepsilon )_(0)(a)^2} . =dfrac (q)(2pi {varepsilon )_(0)a}-|||-(D) E=0 , =0-|||-q, -q-|||-q× ^circ q-|||--a q

U=0 (B) E=0 , =dfrac (9)(2pi {varepsilon )_(0)a} q q-|||-(C) =dfrac (q)(2pi {var

(B) dfrac (9)(2pi {c)_(0)(y)^2} - y↑-|||-(0,y)-|||-+q-|||-(C) dfrac (qa)(2pi {va

(B) dfrac (9)(2pi {c)_(0)(y)^2} - y 个-|||-P(0,y)-|||-+q-|||-(C) dfrac (qa)(2pi {

(B) dfrac (lambda )(2pi {varepsilon )_(0)a}. (C) dfrac (lambda )(4pi {varepsilon

dfrac (qQ)(4pi {varepsilon )_(0)l} C. dfrac (qQ)(2pi {varepsilon )_(0)l} D. -dfr

dfrac (qQ)(4pi {varepsilon )_(0)(d)_(1)} B. dfrac (qQ)(2pi {varepsilon )_(0)(d)_

=dfrac (Q)(4pi {varepsilon )_(0)r}-|||-(D) =dfrac (Q)(4pi {varepsilon )_(0)(r)^2

dfrac (q)(4pi varepsilon oR)-|||-C. dfrac (q)(4pi {varepsilon )_(0)(R)^2}-|||-D.

(B) dfrac (9)(4pi {varepsilon )_(0)a}-|||-(C) -dfrac (9)(8pi {varepsilon )_(0)a}

. _(Y)(y)=dfrac (1)(2sqrt {2pi )}(e)^-dfrac (y{2)} ,gt 0-|||-bigcirc ._(Y)(y)=d