(2006? Wenzhou No.2 model) m Two balls A and B with equal mass, equal charge and opposite electrical properties are connected by eight thin insulated wires Ll, and ball A is insulated by another eight. T 1 and T-left represent the tension of thin lines L 1 and L-left respectively. Taking the whole composed of two small balls as the research object, the force analysis is shown in figure 1. There are two electric fields in the horizontal direction and the vector sum is zero.

The vertical direction is subjected to total gravity, and according to the equilibrium condition, t left = left m,

Find the isolation analysis B, as shown in the left figure. After stabilization, T 1sinθ=qE, T 1cosθ=m, so tanθ= qEm；;

Therefore, the tension of the upper thread, that is, L left, is only related to the gravity of the two balls, and the direction of the upper thread must be vertical. When the mass of both balls becomes left m, after stabilization, tanθ=qE left m, that is, θ changes; Similarly, when the charge amount is changed to left q, the tension on the upper thin wire remains unchanged, but at this time tanθ= left qEm, so θ will also change;

Based on the above, it can be explained that AB is right and CD is wrong.

So: ab.