Two horizontal parallel conducting rods are connected such that a conducting crossbar free to slide along them has a constant current I running through it (Figure 1) . The rods are separated by a distance L and are in an external uniform magnetic field of magnitude B directed out of the screen. The crossbar has a length L and mass m.
If there is a coefficient of static friction between rods and crossbar, what is the minimum current I necessary for the crossbar to move? For the length L of the bar use the notation l.
Express your answer in terms of some or all of the variables l, B, m, the static friction , and the acceleration due to gravity g.