In the shown figure, there are two long fixed parallel conducting rails (having negligible resistance) and are separated by distance `L`. A uniform rod of resistance `R` and mass `M` is placed at rest on frictionless rails. Now at time `t = 0`, a capacitor having charge `Q_(0)` and capacitance `C` is connected across rails at ends `a` and `b` such that current in rod `(c d)` is from `c` towards `d` and the rod is released. A uniform and constant magnetic field having magnitude `B` exists normal to plane of paper as shown. (Neglect acceleration due to gravity)

When the speed of rod is `v`, the charge on capacitor is :