若Qb带正电 Qa带负电;若Qb带负电 Qa带正电;
设AC=R BC=AC/sin30°=2R
由题意可知Ebsin30°=Ea E=KQ/R^2
KQa/R^2=kQb*sin30°/(2R)^2
Qa/Qb=1/8
Qa:Qb=1:8