原题如图1所示,两固定的绝缘斜面倾角均为θ,上沿相连。两细金属棒ab(仅标出a端)和cd(仅标出c端)长度均为L,质量分别为2m和m;用两根不可伸长的柔软导线将它们连成闭合回路abdca,并通过固定在斜面上沿的两光滑绝缘小定滑轮跨放在斜面上,使两金属棒水平。右斜面上存在匀强磁场,磁感应强度大小为B,方向垂直于斜面向上。已知两根导 The original title as shown in Figure 1, two fixed insulation bevel angle θ, the upper edge of the connection. Two thin metal rods ab (only marked a end) and cd (only marked c end) length L, respectively, the quality of 2m and m; with two non-extensible soft wire will connect them into a closed loop abdca, And through the fixed on the ramp along the smooth two small insulating skids placed on the ramp, so that the two metal rods level. There is a strong magnetic field on the right bevel, the magnitude of magnetic induction is B, and the direction is perpendicular to the bevel. Two guides are known