The circuit shown in the diagram contains two parallel rails of length 2L each, attached to a horizontal non-conducting table at a distance l from each other, two ideal batteries with EMF ε each, and a bar of mass m and resistance R that can slide along the rails without friction. The resistance of each rail is r, and the resistance of the connecting wires, as well as the inductance of the circuit, are negligible. The entire circuit is placed in a vertical magnetic field B.

Find the period of the small-amplitude oscillations of the bar along the rails.

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